Referring to people by role in df is fine. I don't know them and won't see them again. Either role or name is fine and not offensive.

It's hard to give advice without being a killjoy. The run sounds a little worse than average for inexperienced players. Abilities like Fluid Aura and sleep are borderline useless / highly situational. However early on players think they should use those abilities because they just got them. I try to work around people until they learn.

I probably wouldn't have said much either, although I would have told them to wait for people before starting boss fights. I would have tried to convince the group to wipe so the ARC could join. "Let's wipe so everyone can fight".

Otherwise if something needs to be said, say it politely, but don't argue. "Please let the tank pull", "Please don't sleep so I can aoe". Whatever it is, keep it simple, don't debate, and pick only one or two things to advise. And if they don't change, work around them in easy dungeons.