As someone who also likes being the MT of alliance raids, your "I rush to boss first to establish myself as MT" genuinely p***es me off.

My approach to MTing is asking "I'd like to tank the bosses, are the other two tanks ok with it? <se.10>", not trying to race to the boss to establish first aggro or claiming to be MT and arguing over it. You made it a contest by establishing your arbitrary rule that not many seem to agree with.

Key to your dilemma is correct communication.