MMORPG's have tried many things, and they have gotten simpler, and the more simple they have become, the larger their playerbase and more profitable it is.
Like I kid you not, the entire point of "mobile" games are so that you spend less than a minute on a level, and thus most are designed as puzzles (eg Angry Birds) or pull pages from old-school BBS Door games where you only had 5 minutes to play per day (such as farmville clones.) As MMORPG's edge closer to mobile games, the skill gap widens.
Early MMO's like Ultima Online, had plenty of things to keep you busy, and you were punished heavily for being lazy. You could steal from and loot other players (because you could do that in all Ultima games, and stealing was a core "fun" thing), thus players formed guilds to watch each others back and take down notorious monsters (which was a side effect of the game's AI and leveling, in which monsters also leveled up when they defeated players.)
MMORPG's seem to the only game where innovations are thrown away in order to make the game less challenging and easier to develop. Yet somehow still manage to underestimate creativity of players. FFXIV has thrown away more than it's fair share.
In a better designed MMORPG, every "real world" concept would apply to content design.
So in the real world, nobody sits around being a damage sponge. So the idea of a "tank" player doesn't come from a military role, but from the "defense" role in sports. The role of the defense is to prevent the opposing team's attackers (for this case DPS), from being able to score a goal. American Football, Soccer, Basketball, Volleyball, etc all have the offense/defense idea built into them. There is no support role in sports. Unless you count the coach and cheerleaders as players.
In a military role, the support roles are armed, but they are only armed to defend themselves, they do not engage the enemy by themselves, they are not on the frontline, that's the role of other people. If you're a doctor, and you are injured or die, you've also killed everyone else. Your role as support is to remain out of sight, and try and save people, not draw attention to yourself.
That is the problem in all competitive online games. Nobody wants to play support, and those who are forced to, play it poorly, so games keep nerfing the importance of the support role until the support role is just a weak attacker role with a mostly unused support kit, and nobody picks them, because that means their scores will be low.
Because it's a game, players do not think about support roles, their real life is never in immediate danger. They see they have a gun in their kit, and mistakenly believe are supposed to use it as much as possible. Yet they see a bandaid in their kit and know they don't need to use it because they're not bleeding yet. Players are thinking in terms of scoring points, not surviving.