There's being undergeared, and then there's wearing stat-less glamour gear in most slots that is then glamoured to look like other glamour gear, plus no earring or belt, and going in as a tank...while having multiple 70s and clearly knowing how gear works in this game. Had he been wearing no gear the effect would have been nearly the same.
Like, I want to stress how much of an oddity it was, seeing glamour gear worn as the equipped gear, including two "Emperor's New [name]" pieces, that was then either just worn outright or glamoured to something else. I'm just shy of 2k lifetime dungeons run on this character, and this is the first time I've ever seen it. This was not undergeared - this was straight up wrong gear entirely.