@OP it's pretty pot luck. I had a really smooth EV GroupFinder run where two people didn't know the op at all (1 dps, 1 healer), no voice comms, and all typed instructions. Then I had a pretty rough KP run where only 1 person fessed up about not being there before (melee dps), but it was obvious there were at least 3 others in that run that were clueless (2 tanks, 1 melee). Really depends on the personalities on your server.
I genuinely suggest that nobody queues for Karagga's Palace with the group finder - unless they know the Heavy Fabricator puzzle inside out.
That fight is SEVERELY overtuned for a random pug because there are way too many things to keep track of, you won't figure out the puzzle on the fly and the enrage timer is relatively tight. It's the hardest fight in the game outside Explosive Conflict and even with a guild with voice communications it's really tough. Without Vent or Teamspeak it's impossible imho - unless, I repeat, someone knows the puzzle inside out and can do it with his eyes closed.
Oh it's not overtuned, it's fine. If you see above, I had a really rough KP, no voice comms, all typing. Yes it took us a few tries to get through the puzzle boss, but that's part of the learning. We were too worried about the enrage and overcompensated by having 2 clickers, and more dps on the floor. Went with 3 clickers and it was fine.
I tried to take a group of 8. Queued everyone in the group finder. Didn't get comms. Big waste of time.
I believe that's working as intended. If you join the Group Finder with a full (4/8) group, you're not adding anyone from the pool and therefore not actually using the GF, and thus no comms for your group. I'm not saying I'm right, just a gut feel for the spirit of the tool.