So this isn't what this thread is about but.... there are always 2 magic damage users in the group 100% of the time. Other magic damage users that get forgotten about are dark knight and ninja. Please play foes.
Or healers. Healers that especially love to DPS during downtime will always welcome Foe's Requiem.
EDIT: There's a ton of other things as to why players may be playing poorly. An embarrassing thing for me, but I remember when I started out, I had no idea Shroud of Saint gave me MP back. I had never encountered what "Refresh" meant; it took a very long time for me to notice it gave me back MP and no one had told me and I'm pretty sure this game makes no mention of what refresh is. Any time I see a healer struggling with MP management, that's one of the first things I'll tell them. I've gotten so many thanks just for telling them that small thing.
I don't think they need to completely gate content behind a Stone, Sky, Sea performance rating. Everyone should have the option to participate in all content regardless of skill level provided they find a group to go with them.
That being said, I would like to see an option in party finder and raid finder which would allow some level of exclusion based on performance for people who are more experienced and better at their jobs (Similar to what OP is asking for). Nothing is more frustrating than sitting in party finder until you fill up only to find out that one (or more) of the players has little to no idea what they are doing at the most basic level.
Since this would only be for party finder and raid finder, the vast majority of content would not be included in it. The only things that are queued up for through raid finder are Savage level and current Extremes which is really where the problem is most perceivable as everyone must be able to play their job to a slightly above average level to have a prayer of completing the duty. I would never advocate for people being locked out of dungeons or MSQ as they only take a bit longer with sub par players and are 99% completable by any random grouping of 4 players.
I suppose I'd be somewhat safe in assuming which forum this poster visits most frequently and how high his bar would be for this rubbish suggestion.
S^3 is good as things stand. Even if SE acceded to this ridiculous request, I'm almost certain your type won't be satisfied with that. In fact, none of you will be satisfied until the 5-10% of you is all that's left in Eorzea.
Eh, just add a Proving Grounds proxy and have it be a barrier to raid/current dungeon content. Or differing difficulties thereof applying to differing content (1-30, 31-49, 50, 51-59, etc.). Where is the problem here? Not like I don't deal with bad players already. If someone asks for advice with a leaf above his head, in a SB instance, I'll happily oblige him. At least that "bad" player has the intelligence to ask for help with stuff. Beats having a manchild in current content lose his mind over being told to use cooldowns when they pull half the instance.