Peltasta and Rod3, by nature, have more defensive capabilities than most others. So you'd be allocating your stats accordingly. Personally, I don't like having more than 100 con. Around 70-100 con is fine. Even 50 would be alright to some extent. You can get gems and different armors to help that specifically. Or even allocate more stats into con and have your armor be more offensive based with high level red gems. It's all a matter of opinion. If you feel you need more damage, allocate or equip accordingly. This build specifically is to make murmillo the strongest it can be. Assuming Murmillo can go to 3, this would be making the most of murmillo3. As far as future proof goes, this will be viable at whatever and wherever. Is peltasta 2 and 3 that important to take over others? Again, a preference.
Putting it in context to everything else is a little easier. You get tankier with Peltasta 2/3 but is it incredibly important to take it as opposed to taking Barb2 or High2 or Hop2? Barb2 alone is not good enough. Barbarian, in my opinion and may be the general consensus, is either a 1 or a 3 class (previously a 0 or a 3). You either take 1 or take 3. Pouncing, Frenzy's C3 attribute, Slash debuff. However, you still get one of barbarian's best moves, Seism. Hoplite2 is good enough as you get 100% uptime on Finestra and Spearlunge. Hoplite3 isn't necessary though it is a decent and viable upgrade. Highlander2 is alright as well but Highlander3 gets Vertical Slash which is getting a pretty substantial (relative) buff.
So summarizing all that: As a Rod3, you won't have access to another 3 of any class but Peltasta (get tankier and some offensive capabilities + Swashbuckling 15) or Swordsman (good PvP). I don't suggest Barb2 or Highlander2 as they are both sub-optimal since you don't have access to 3. However, both are viable: Barbarian's Frenzy and Seism and Highlander's Skyliner, moulinet, and crosscut. Hoplite 2 is good by itself but offers very little synergy with Rodlero and probably murmillo (slash debuff and most of Rod's moves are Strike type whereas you get Hoplite's pierce + stabbing and pierce active skill).
As for fencer, Fencer's are an evasive frontline. Rather than wanting to take damage, they'll evade the damage due to esquisive toucher or whatever it's called. This makes them one of the most efficient frontliners in the game, perhaps even better than Rodleros, Dragoons, etc. Perhaps being the keyword. It depends on how much you want to invest in dex as a fencer. Full dex isn't necessarily a good idea as it just doesn't scale well as a swordsman and stronger monsters will have harder to evade things where magic damage is impossible to evade (making fencers very susceptible to that kind of damage which is in abundance late game). Because of this, you'll want to take a shield to mitigate that type of damage. We don't have a lot of information on c8 fencer other than a gif so the details of epee stance are ambigious. On that note, as fencers already have one specific weapon dedicated to it, I don't think it's likely you'll be limited to a specific secondary. On top of that, a lot of other classses' skills have the ability to use rapier and shield.
The hoplite comparison isn't that good or even apt. Hoplite is strong by itself, don't get me wrong, but it's not the be-all-end-all of it. Dragoon and Catas into Lancer or Dragoon2 both use 2handed spear because 2handed spears are better than 1handed spears in which case, they won't have access to a shield unless you weapon swap.
Summarizing, I'd leave dex at around 100-130. You can better sort this out with your armor. Esquive Toucher already lets you dodge and fencers are more offense-centric than other swordsman classes so taking a shield isn't optimizing the inherant advantages Fencer has over other classes. On top of that, Rapiers are made of dog shit. You don't want to be taking too much damage anyways or they'll break constantly. Also, there will be times when you'll have to take a shield so having one is always a good idea.
The reason I didn't mention fencer was for 2 reasons, I forgot about fencers and that they are also a bit of a meme. In theory, they should be fantastic late game,"tanky" with amazing return damage plus great inherant crit amplifiers and a pierce debuff that synergizes extremely well with their kit, but because of how you can't dodge magic attacks, they're weak and almost all late game content have some variation of magic damage. Rapiers, like i said, break too often so you have to have 2 of the same sword.