We've been able to run Grand Company Squadrons through multiple ARR dungeons before trusts, including old totorak. The problem imo was that all the optional detours and odd mechanics often slowed down runs considerably when we had people new to the dungeon, and it made getting those on roulettes annoying.

I'd guess dps/tanks getting more mitigation and self-healing was also for roulettes too. It makes healers less a point of failure in something players of all skill levels run daily.