I really feel a lot of these claims have come from bandwagonning. That is not to say that there aren't parties that will disband or kick if the first soar isn't skipped- there are. However, those parties say they will do that in the very description. Don't join those parties if you can't meet those requirements! I see less and less of these parties and more "know how to handle soar and tether please" parties. I'm even in the datacenter with Gilgamesh and Balmung, too; the two servers that probably really pushed for those requirements the most. You make it sound like it's a majority of the community, and it's not. It's a portion of the community demanding this. I really wish people would stop blowing issues like this out of proportions.
Also, how will you know if people can or can't do things without trying? Also, if you approach it with a negative attitude, you've already set yourself to fail.
Onto another relevant topic, the OP is a new player to the dungeon, but not really a new player if they're hitting level 60, end of 3.0 base story. The basics of the game are not new anymore. While I don't mind people going in blind, but if you're going to ask what to watch out for, why not ask Google that? For the sake of the argument that there was a mentor- yes, I am aware. You can get mentorship very easily, to the point that you don't even need the majority of dungeons previously done. As people have pointed out, you can easily farm up the 1,000 needed dungeons doing unsynced content. What if the mentor didn't know either because they never did it before? We have ourselves a little paradox here!
While people are quick to point out flaws with the mentor system, this often gets overlooked. You can put on the crown and queue for dungeons normally and still keep the crown. Or you can use mentor roulette and be forced to wear the crown into a random dungeon- but this requires you to have most dungeons completed. However, my main point was to call to attention the previous paragraph and the fact you can queue normally with a crown and appear as if you used mentor roulette.
Just a thought provoking observation there.