Okay here's a rundown of what your friend is talking about.

When you do the final dungeon, people aren't gunna be so, gunhoe about rushing through things because there will be plenty of people like you. There is some of this behavior you refer to happening here but for the most part those people are going to be overruled. On the other hand, after the story, hardcore dungeons like Ampador keep and higher, you'll unfornately see people become more unforgiving, because what those people are doing is grinding for their AF2 armors as well as weapons and sets for the primal fights. And they need to alot of dungeon grinding because I believe the cuirass of AF2 is around 480 tombstones worth, and each dungeon raid gives around 40-60 tombstones at ampador keep anyway. As a tank, you won't have much problems grinding, but DPS on the other hand probably will.

Honestly though, your not going to see much of this behavior before the lvl 50 dungeons so I think it going to be not much of a problem.