Skyforge, while in closed beta at the moment, sounds like the type of game you are looking for. While it does have classes, you can freely switch between them when you unlock them, also no levels, just prestige.
The devs claim that there are no levels in TSW. Though there are no character levels there are still gear levels. With the absence of character levels all the players just moved to using gear Quality Level as the unit of measurement. So instead of saying hey we are doing dungeon X you need to be level 60 to do it they say hey we are doing dungeon X and you need QL6 gear.