It only makes sense to you because you're stuck into thinking raids require the Holy Trinity in a game where it doesn't.
And why are you bringing up TF2, a game which is fundamentally different? The reason TF2 had classes was because they were restricted in what they could do. Defiance is not restrictive beyond what Perks each individual has chosen.
TL;DR: This isn't the game you're looking for. Might I recommend WoW, Rift, TERA, LOTRO, or DDO for you?
I dunno.. Set classes would require tanking and aggro skills or bonuses to the BMG gun for healers and that sounds like it would corner me into a hole, which is what I wanted to get away from to begin with.
Cause let me tell you, when you crit a few times in a row with a sniper, the boss type mobs get very angry at you and ignore the man with the shotgun in their face to come straight for you. Its then I swap to something more fitting as he comes closer or I just stealth and get more distance.
EDIT: I totally forgot about the BMG I carry as my secondary! Just in case! For those times Im either out of ammo or the team needs healing.
I chose this game over another that had similar gameplay and one of the main factors was no classes. I like freedom and always feel so bolted down with classes.
I'm really only referring to I wish each class had it's own unique trait, move, ability, something that set it apart from the other models aside from being nothing more than another character model.
I'm not referring to each one being it's own actual class like tank/healer/dps/etc.
The game has tank/healer/dps you just have to equip perks for that. Since you have limited amount of perks you can't do everything all at the same time.
Players that play in Coops with friends mostly will specialize in a certain role by choosing their perks and loadouts. Most others will most likely use a more general perk set and just switch weapons. It is all rather simple in Defiance. A little too simple maybe.
Different classes add to replayability. But since Defiance has very little of that in the first place, it is just too small, that does not matter. It will be interesting to see what happens when the new race is introduced and players have to run through the same quests again. At least that is what I expect.
There are a few bonuses based on class in this game. Im only ego 405 and im seeing items that increase damage based on what class you chose, minimal influence of classes imo, but at least there is something there.