The problem is that you usually have the choice between going in solo and hoping that people follow, and standing in the healer-dread wall forever.
If you go in solo, you die. If you stay in the blob, the game is incredibly boring. People want a game where they can do things and feel smart. Stuff like flanking, backstabbing single people, sneaking up on someone and ambushing them. That has nothing to do with you being OP and being able to kill everyone. It means being able to actually make decisions which have consequences. Playing good and being rewarded.
In the turtle modes, the game just doesn't work that way. You blob up, and you get rewarded for not doing anything interesting. Just hang about. Shoot stuff. Wait for the enemy to do interesting stuff, because that interesting stuff makes them die, and then you win.
To me, dreadnought is at its best when people are split up, and there are fights all over the place. You can still cooperate. But cooperation doesn't only come in the very unequal flavours of "stick around a healing blob" and "convince your whole team to do the right thing simultaneously in a perfectly choreographed action to break the blob. Also hope they actually have the modules necessary to do so". One of these two is easy to perform with a random group of players, the other is not.
But mostly, i just don't see what healing actually adds to the game. Being a healer is boring as sin (And i am a person that usually has an affinity for healer classes). You hide behind some wall, and press 2 and 3 on cooldown. You can also use your guns if you want to, but that isn't that necessary. Press shields when you hear the nuke sound. And being in a game with lots of healers is also boring, because nothing dies.
Also, the censorship filter on this forum is rather annoying. The same spammer manages to spam with the same stuff every day for weeks, but i am not allowed to use the opposite of heaven in a sentence. Weird american religious sensibilities.