Hey there, thank you for formatting the list the way you did, its nice and easy to read.
So I generally like what you decided to bring, and I generally dislike what you decided to arm them with.
I'm a big iron hands player and I'm going to pick apart your list a bit here, since this is /r/warhammercompetitive after all, but its not a personal slight! I wont be recommending picking an entirely different chapter to be more competitive, for example, so no worries there.
Disclaimers underway, let's get to work. This is long.
What's with the plasma pistols on all your characters? All of the dangers of plasma, none of the range or rapid fire. One or two on some secondary characters or sarges I could see, but you've got them everywhere. Consider having two at most, and none on your primary characters. If one of them overheats, it could give kill points for free to the enemy or a tactical objective assasinate card, etc.
Your HQ isn't well equipped. He has storm of fire, so he's going to want to be standing still near your long range firepower, but he's on a bike, so which encourages him to move... He has a thunderhammer, so he wants to get into combat - but he doesn't have a stormshield, so he's vulnerable to one solid attack once he gets there. And he has a plasma pistol, which could very likely kill him as he is your warlord. Err...not good. Back to the drawing board for this guy. I personally love biker captains, so just reconsider your wargear choices for him.
Your LT has a plasma pistol, so he wants to get in close, but he has a 6" move, so he won't be getting close to anything. Plasma pistol is 12" range, so you can - maybe - threaten deepstrikers with a single plasma shot that has a chance to kill your reroll wounds aura character. Or, you could spend two points less, and take a mastercrafted bolt rifle. It has twice the range, twice the shots in rapid fire range (or max pistol range) and does 2 damage out of the box without overcharging. Honestly- this is a no brainer. If you want a cheap LT, which I assume you do, save the points and take the MC bolt rifle.
Moving on to troops, the IH chapter tactic is best utilized with Primaris, with their two wounds and all. However, scouts are way more points efficient and can deploy outside of your deployment zone, which is amazing. All of the points you saved by taking scouts is lost by taking an extra primaris intercessor squad. If you want to take primaris, I would actually suggest that you do, since I rather like their profile, drop a scout squad. The more competitive option would be to drop the primaris squad.
If you do take the Primaris squad, the power fist or chainsword is better than the power sword. Since primaris have 2 attacks base and 3 on the sarge, the powerfist is a good choice to take advantage of the extra attacks on the sarge. Obviously, the chainsword is free- so you can't beat that in efficiency. If you do take primaris, consider making their squad a weird number, like 6-8 models. They're a relatively durable screen that can still reach out and touch targets with their long range rifles, and a couple extra models makes them cover extra ground to protect your long range shooting.
Vanguard Detachment:
Drop the plasma pistol on your librarian and take a stormbolter and a jump pack. You have null zone, which is a great power, but how will you get in range to use it? The jump pack on librarians is really good- it gives you the movement you need to get the librarian into position. You can hide him behind cover, and fly over it next turn to pop null zone in the center of the baddies line, or you can fly him in just the right spot so that the enemy warlord is the closest visible model to smite, etc. When he's on foot, he can't do any of that, and when he's in a transport, he's not casting spells - and if your transport dies and he's the only model inside, you better not roll a one...
For the contemptor.... I don't like the basic contemptor model. Yes, it has more wounds, an extra point of strength in shooting and CC, a 5++ invuln and from IH a FnP, but it degrades. And the degradation is a problem. The second it hits that first bracket, its now got the ballistic skill of the cheap-as-chips normal dreadnought...but the contemptor is quite a bit more expensive. If you get first turn, you are still hitting on 3's since you're very likely deploying further than 24" away...so you gotta move to use the assault cannon. The extra strength won't matter if you miss!
The venerable is 11 points cheaper, but it fires at full ballistic skill until it's dead, and it can take a wider variety of loadouts as well. Additionally, it can pop smoke, so if you still need to move it, you can move, advance, and pop smoke turn one so you can get into range . A -1 to hit works out to be the same (if not better, army depending) than a 5++ invuln. It also has the same toughness as the contemptor, so people will have to expend the same firepower either way to take either of them down. While it does have one less point of strength in shooting, that let's you focus on softer targets like elite infantry or screens a bit more efficiently, as the s6 wounds the same targets on 2's/3's as the strength 7 kheres. You can wound rhinos and razorbacks on 4's, but... I dunno, I'd rather charge them with any dreadnought and can-open them, versus peppering them with one damage shots they have a 50/50 chance to save.
For the ironclad, consider taking a hurricane bolter. Dreads benefit from the bolter discipline rule, and 12 bolter shots at 24" is pretty damn good. The ironclad is going to be footslogging it up the board, and just about everyone is aware of how scary it is - so they're going to avoid it. Having some bolter shots lets him participate until he gets into close combat, and, more importantly, lets him clear a screen that would otherwise prevent him from charging something he wants to crack open. If you take the hurricane bolters, you can use the points you save to get the iron clad assault launchers which gives your SM army a rare source of mortal wounds. However, some people like the melee weapons as they can pop smoke without worrying about anything...its up to you on this one, mate.
About the redemptor, take the onslaught gatling over the heavy flamer. just trust me on this one! You dont really need the charge defense, as the redemptor fist literally hits as hard as a lascannon. Take the extra dakka to clear the screen that would otherwise prevent you from charging something. The gatling has 6 shots, instead of d6, and three times the range, hitting on the same strength, ap, and damage values. The flamer is autohitting, but 8" range is hard to get in on, and you might only roll a 2 or a 3 for the number of shots.
I love the sternguard squad - they're great models. Hard to deliver - a droppod is nice, but expensive in points, (the models have never been cheaper on ebay though!) but alternatives like rhinos have a chance of dying on the way in.... up to you. I think whatever you were planning to do with them is great, honestly.
For the LT heading your spearhead detachment, consider swapping him for a captain. Your warlord is a captain on a bike, so he doesn't really want to hang around your gunline as much as he wants to zip around and charge into stuff. So, take a cheap captain for the reroll ones aura here.
I definitely like the two devastator squads. It's popular to give them one or two extra, plain bolter, marines to act as some meatshields for the heavy guns, in case they take some long range fire. It's fairly cheap to do so, so I recommend it. One thing I'd change is the plasma cannons for lascannons, or at least missile launchers. It's points expensive to do this, I know, but the d3 shots on the plasma cannon will bite you in the ass more often than not- but more importantly- missile launchers and lascannons have an extra 12" of range over the plasma cannons, meaning your target will have a much more difficult time hiding their armor.
I like that you took a predator- no IH list is complete without some sort of armor!
For the fast attack, the bikers need to be changed up. I personally prefer the melta gun on the attack bike, since it doesn't overheat and the bikes are fast enough to get into melta range, but it's up to you - melta is expensive. You should definitely drop the plasma pistol on the sarge in favor of either a thunder hammer, storm bolter, or combi-melta/plasma.
Finally, for the razorback, the lascannons are a bit of a trap in my opinion. You already have devastator squads that can take lascannons, and they're not going to be moving and transporting something unlike the razorback. If the razor has to move, youre hitting on 4's, or worse if you're degraded, which is easy to do on a t7 3+ save chassis. I have had surprising success with the heavy bolter option. I know it doesn't sound like much, but try it sometime- just run that sucker up the board and see if you can use the movement of the rhino to get a toe into close range with a character, and blast them with 6 heavy bolter shots. Everyone sees a heavy bolter razorback and pretty much dismisses it, but 6 HB shots threaten just about everything in the game - for 17 points it lets you take heavier firepower elsewhere in the list.
Still with me? Whew, that was even longer than I thought. As I said before, I liked what units you brought, I would just change their loadouts. I'm not a huge fan of plasma, as you can tell, so if you want to stick with it - go for it! I would just aim for more rapid fire sources of plasma over plasma pistols, if you're going to do that. So combi plasmas, or just plain plasma guns, or better yet hellblasters, would be great choices here. I'd stay awaay from plasma cannons and plasma pistols though.
Good luck with your IH list! Thank you for reading!