Absolutely, you gotta try them first. Don't be shy. See their attitude. Then decide. Offer actual help, like pointing out exactly where he can get the replacement gear.
If it's MSQ with 8 people and you noticed his underlevelled ring though, that's a bit awkward (I mean, you click everyone and scan their gear..?) so don't say it in party chat, let that one go. He's probably having a bad enough time being pressured to skip all the cutscenes, or still pressured if he didn't.
If you are going to point out a valid point though like a caster ring on a bard, then make it funny, humorous, and quality writing. And they can still tell you to shut up because they are having a headache at that time and honestly that by itself is not a vote kick reason ... Just think of how they will feel after the bossy mentor vote-kicked them because he said he had a headache and just wanted to clear the dungeon.
So, you realize as a mentor you are there to help. Nothing was required of you, nothing expected of you. You don't have to be the efficiency police. You are not the efficiency police. You are there to "help". So if you actually can help, then it's a minor miracle. The devs and GMs should come out like they did on Moonfire Faire and thank you. Realize that it's not easy, nor required for you to even help, much less be bossy while at it, as long as you are actually "helping". But don't go off shielding the sprout from harassment just yet ... you will only start fighting and bossing at the harasser. Defuse the situation. Simply be the help, not perform the help. Realize that being of "help" means making the run more enjoyable for all. Reach that state, achieve enlightenment ... and argghhh I can't make this stuff up anymore. xD You see how one can literally say anything and not make it seem bossy now? While enclosing the truth in what they say? ^^ Good luck. Hope I was of "help" xD I mean, in the end, they've gotta help themselves.