The tanks job is to hold aggro on enemies > mitigate as much damage possible being received from those enemies > maximize damage output while doing the first two.

All of these things are indeed the tanks job. Some of the tank jobs do some of these things better than others. Tanks that refuse to do these things by limiting themselves to imaginary "role restrictions" are just limiting their contribution to the team. A good player will try and maximize their output in favor of the team in every way possible. At the end of the day efficiently clearing content is everyone's job. Those who are refusing to give their all to this end are holding the team back. This isn't just applied to tanks.