Except that's usually what happens when anyone (mentor or not) tries to give advice to those performing on a sub par level. You yourself quoted LunaSnowfield's 3 points, number 3 being how SMNs either use just one DoT, or none at all. And when you try to kindly tell them "Hey, you will do more damage if you use Bio II, Miasma, AND Bio, and Bane them to the entire trash group," they retaliate with things like "You don't pay my sub" or "I play how I want to play, you elitist prick." So Mystery brings up a valid point; this isn't projection, and I think you may want to refresh yourself on what the definition of projection is.
While I have never partied with Mystery (to my knowledge anyways), they hardly seem the type to play poorly, and then turn around and accuse others of playing poorly while ignoring their own poor performance. If they did, that would be projection. However, their comment you quoted in bold is not.Psychological Projection: a theory in psychology in which humans defend themselves against their own unconscious impulses or qualities (both positive and negative) by denying their existence in themselves while attributing them to others.
This including blame shifting.
Limit Breaks going to waste fall in the same boat as DPS not playing their class to, at the very least, the most basic level. My own personal rule is, if a melee does not LB before 10%, the minute a boss (in any content, 4-man, 8-man, or 24-man) hits 10% HP, I LB. Yes, even if I am on bard, I use my weaker ranged physical DPS LB. Because why waste it? Especially in 24-mans where it goes away the minute the next boss is pulled? If melee get mad about a ranged using the LB, well, that's not my problem. They shouldn't just leave the LB sitting there, and LBing at 1% is just as wasteful as not LBing at all. This is my opinion.
A dragoon doesn't want to use Heavy Thrust? Well, there goes a 10% damage increase to their entire rotation throughout the entire duty. A bard doesn't want to use Wanderer's Minuet? Minus 30% damage to their entire rotation throughout the entire duty, plus they lose access to Empyreal Arrow and Iron Jaws, which are staples in a bard's rotation at level 60. Healer doesn't want to DPS? That's easily 10-15% total DPS in a duty. And all of that can add up very quick.
And again, it's not elitist, nor is it projection, to expect others to carry their own weight (yes, even in Duty Finder), and refuse to carry entire parties through content. I will gladly eat a 30 minute penalty (which I can spend time crafting or gathering, and be for more content and far less irritated) if it means I don't have to carry a party through easy content (or really, any content). That's not something I find particularly enjoyable, and I won't be called an elitist for refusing to carry. And I don't consider it to be QQ-ing to eat an penalty rather than carry players.