Prepulling mobs as healer

[Penthea]

Yet several times I've heard tank or dps get mad and tell me to stop prepulling, even when they had ignored my request to pull more.

Request.

No one is obligated to fulfill your request.

I don't mind at all if tank wants to keep pulls small, but they should also not mind if I go pull mobs and bring them to the tank. They literally don't have to do anything except their aoe rotation, which they are doing anyway.

Clearly you do mind if they pull small packs given you end up pulling more yourself anyway and force the tank to deal with the result of a multi-pack pull.

Why is prepulling considered rude/bad in this case? Everyone is completely overgeared to the point they may solo the entire dungeon.

Because your actions are telling the tank "What you're doing isn't good enough for me. You didn't do the thing I asked so I'm going to force you to do it.".

If you are incapable of handling the monotony of single pack pulls I suggest finding a tank buddy to do dungeons with, instead of being a bit of a diva with pugs.