Actually, you are mixing two points here:
Well that is if you consider plate too powerful, it has a drawback (speed), and that is a balance problem and not a genre problem.
This is true - there are certainly other ways to balance plate besides a prohibitive cost.
In rpgs you have character progression and even special items, so a player can be powerful but everyone can eventually progress to get the same power (the game has to be fair, again not a genre problem).
Well, no. That only works for games where all those powerful players play together on one team (e.g. against NPCs) and not against other human players.
Imagine some CRPG without the recent patch in a year of time. ALL players who are still playing the game reached max level and max items (because they are not competitive otherwise).
Now, a newbie joining would have to play for 30 levels without ANY chance to contribute anything to the fight. You think he will do so? I don't. There simply is no endless amount of fools that agree to be cannon-fodder for the in-game gods, unless those fools are computer-generated NPCs.
And don't fool yourself - every game going that route will earlier or later end up like this (probably earlier, because there are so many no-lifers out there).
I'm not talking about pve or pvp at all, just about the game structure, if you want a pure fps, there's native already, no need to make a mod and then modify it to be a clone of native mode.
You are talking about the game you imagined crpg to be - namely something like WoW. Well, it isn't (luckily) because chadz prefers a PvP game.