Skills should scale down in lower content NOT be greyed out.

[KyahAlmasy]

Repeated for posterity.
Catch 22, both scenarios will piss a ton of people off.

This is not a good idea.

The best solution is to make more skills available at lower levels.
Every tank/dps should have an AoE, and at least 3 single target skills (whether thats a 1-2-3 combo, or 2 GCDs and an oGCD, or a GCD a DoT and an oGCD, whatever) by level 15.
Every job should have their job gauge and a substantial rotation by level 50.

I've been playing since FFXIV originally came out, and I can say that I have never seen anyone vote dismiss in a low level dungeon, or try to kick a sprout for being new. It would would take far more time waiting through the leaver penalty (30 minutes) and then a DPS queue (likely another 15-20 minutes) than it would just running the dungeon with them. It just sounds like the most inane, and backward thinking from a progression, and time-saving perspective.