don't get me wrong here, but i think you're probably supporting wrong. supporting isn't actually just placing wards. I mean, i play EXCLUSIVELY 5 pos support (more like 6 pos actually) around the 3.5~4k range and i never (literally) had a teammate flame me. what i noticed from your text and from my experience:
1- Heroes :Jakiro, disruptor and rubick are really bad to play in the 5 pos. each one of them need some sort of item, like positioning and mobility for rubick and disr, tranq euls for jakiro .you might get that force/blink eventually, but i find that when you finally do, you fed too many kills already. That way, i tend to settle for more item and level independent supports, like vengeful spirit. not only she doesnt need farm and levels that badly (i find that with level 6, tranqs, stick and medallion i'm good for the rest of the game), but you can mess up the enemy team positioning with swap, and keep your retards alive too. omni also works in a similar manner. i tried to do that with dazzle too, but i think he is too level dependant. but you might wanna try it, anyway. ( i only do it radiant, because of the easier exp from pulls)
2- Vision: deward. like, reaaaally. i think that, aside of me, i only ever got matched with 2/3 other players that actively look for enemy wards to deward (excluding the obvious rosh/rune ones). negating vision is almost as important as getting vision. if you're a better player than your enemy, you can act better than him, in case you both don't have vision. Also, ward creatively and adapt the warding for each moment of the game, depending if your team is in the aggressive/defensive.
3- Early game: starting items are important as fuck. as i already said, i go for 5-6 pos support, so i buy both courrier and wards at the start of the game. also 2 sets of tango and a clarity or a set of tangos + sentry. i give one ward and one tango to the offlaner and 2 tangoes to the mid player. i found that, playing selfless allows your team to play more greedy or have one core more. as most pubs go to late game, you get an advantage. try to contest bounty and give it to your carry, try to zone offlaner, get the most out of your pulls.
4- Farming: learn to last hit. not like 60~70% but actually 100%. i think that last hitting as a support is more important that last hitting as a carry. As a support, you're gonna have little to none chances to get those creeps, so each one that you miss is a significant part of your networth. not to mention the income from pulls, that if you get 100%, your gpm can go through the roof (for support parameters). i also not ashamed to tp to an empty lane (after asking if my carries want that) or farming in more dangerous locations, if not just sapping exp. 5- Teleports scrolls: i think that everyone knows that you should have them all the time. it is actually THE first item i get, before boots even. enemy team diving an ally? tp to that tower, even if you KNOW you can't save him. chances are A)even if he dies, he will be thankful, because you at least tried, and trust his team better, B) your tp scares enemy, ally lives, C)he dies, you get to enjoy 30~50 seconds of exp and some farm. 6- Positioning: you should be in the outskirts of the fight. drop your combo, retreat, wait cd, rinse. you should try to tank some skills too, but as a sup, you can't tank shit. you're probably dying if you're not an ogre or omni.
Anyways, i that is what i found from experience, hope it helps you. its hard to play selfless, but i think it pays off: i created a new account and i'm enjoying 75% wr over 70 games. Dotabuff: http://www.dotabuff.com/players/96903730