Would you like an in-game parser?

[Reynhart]

Tanks have to know their class very good or they die.

To the point where, to clear content, every tank had to withdraw their tank stance as much as possible, avoid any tank stats back when it didn't increase their DPS. So, basically, anything but tanking.

Healers have to know their class very good or all die.

So, from now on, you're a bad healer if you don't pop Cleric Stance the second no one needs healing, even if you didn't let anyone die or keep a bad status effect during the whole fight. So, again, a thing that as nothing to do with healing

Why should damage dealers be the one role, that don't have to know their class?

There is a difference between "not knowing your class" and being 10% below perfection, which in these days, means you're absolute garbage. Even if you're avoiding every mechanics so that you'll go easy on your healers. Black Mages are even encouraged to stay in AoE if avoiding means lowering your DPS by a tiny bit. So, if you do anything that is not DPSing, there you're bad.

The worst part, of course, is that this mentality has poisoined every party for every content, even though thoses 10% are actually meaningless for most content. And now that people think like that, there is no going back.

And these have to be on a similar skill level as tank and healer skill checks.

And, by the way, tanking checks are ridiculously low compared to DPS check.