It's not gear that's the main problem, I've seen well geared players in SM not knowing their roles especially tanks not kitting bosses correctly (i.e. for fabricator in KP) and even seen some people doing stupid things like running into the lava pit full of dogs in EV just before gharg and when revived running on straight to gharg without waiting for people to ready up without knowing tactics.
I think for group finder there needs to be some sort of skill scoring before you progress on to each operation, maybe even some sort of training op before you can do the story modes then having to finish all the SM's before progressing on to HM and so on.
The problem is (and was probably before GF with pug groups) skill and experience.
If the problem is skill and experience, then they are only going to get that by doing that operation. Making it hard for them to get into that operation will only work against that. Something like a skill score is impossible. How would you increase that? By successfully beating bosses? First of all that doesn't tell anyone if you're really a good player or even if you understand the mechanics of that boss. Second of all, how can you increase that score, if you need it to be at a certain level to enter the operation.
It's like it was in WoW with gear and achievement requirements. If somebody wanted you to have gear, that you could only get in that raid, or the achievement for completing the raid, it was hard for new players to even get that, because the groups that you needed to get into to get them required that you would already have them.
WoWs raid finder sets a pretty good example of how they can teach you how the bosses work. It's very intuitive and it works as a training ground to teach you the basics. That only works in WoW because the difficulty is a bit lower and you can get the right gear for that raid in like a day.
Sorry for late reply (which my post is quoted above), but the problem I see with group finder groups rather than premade PuG's or guild runs is not just lack of understanding of "specific" mechanics but generally the awareness of how endgame content works. For example for the fresh 50 the only Pve content they've done up to that point bar fetch quests are the class missions and normal flashpoints which are too forgiving on mechanics to the point where someone can agro mobs, stand in circles, not interrupt, faceroll their abilities etc.. and still get through it all.
They then get to endgame and have a huge slap in the face, because what they were doing the last 50 levels was the wrong way to go about it and they now have to be careful, however for the experienced and geared player who knows how things work they shouldn't be limited in what content they can choose to do because some 50 is still learning the robes.
What needs to happen is sorting the riff from the raff, ideally by giving everyone who chooses to do content by group finder a quest or task. For example the simplest way would be to give everyone a quest via GF to complete all HM flashpoints and both SM ops at least 3 times to unlock the next tier of content and maybe even get a nice comms box as a reward for doing it. If anyone can do that they should be geared enough as well as competent enough of raid awareness and how mechanics in "general" work to progress on to the next tier of ops. Anyone who can't is simply not ready.