Just watch the lord of the rings, tell me whos tanking, whos healing and whos dpsing, then get back to me and talk about party composition needing to be set in stone. It is about making the game dynamic.
All you are presenting me with are supositions
"And since everyone can be anything, odds are the monsters will become such stat bloats that you'll need MOAR DPS".
It does not need to be this way, not that its a bad thing if everyone turns out to be good at doing damage, but the monsters can use their own tactics to keep themselves from dying too fast, like penalizing attacks when they take a certain stance or temporarily disabling some of the members of the team, etc. These are just examples i came up with in a second, im sure you can think of more if you try.
"As an aside, dps race is avoided all the time. There are only some choice encounters which are straight out dps races, anywhere else there's the mantra of 'better alive than highest dps for 5 seconds after your death, dipshit'."
Yes and no, when presented with the choice of how to face an encounter the ones that will be fighting on the offensive and the ones that are supporting on defending can change according to they own skills and strenghts (that theyve picked, like perks, weapon, armor, magical trinkets, passive bonuses, etc). you keep player tasks/role new and fresh, keep your players actually playing a game instead of repeatedly mashing the same keys.
"If there's a lack of variety in encounter design, its because MMOs like WoW are structured around the whole theme park paradigm. Not because there's one class dedicated to healing and who is pretty much necessary for a lot of the game's content. Old sandbox MMOs often had that." True, yet you seem to want to play the same games with updated graphics and a different log in screen.
idonthavetimeforthiscrap not every player will have the stupid amount of time necesary to max out their character, but having 2 warriors, both using one handed swords just as well, but the second warrior being able to also use bows because he invested time the first player didnt have on it will not automatically make the first player useless, while at the same time rewarding the second players time with flexibility instead of outright giving him power. Level might be a factor, but im not taking it into account because it is not what we are discussing.