In a 12-person UQ I never really see there being an issue with people having less than ideal gear. If they die, there's always people there to rez. The only time I've been close to wiping so far is when we don't have enough people or it's a new UQ and we don't know the mechanics. And even then, we still didn't wipe. It's very forgiving imo.
However, I do recommend doing what you can to gear yourself, especially going into SH. The difficulty scaling is really shitty until you get closer to EH, so you'll be less likely to die on the spot if you have decent equipment and understand your class. You probably won't drag your party down if you don't, but you'll have a much more enjoyable experience overall.
I could be wrong but when player die, doesn’t it bring down the rare drop rate?
I still believe this is the reason for guild involvement. This would solve this problem.
Only if they don't get rezzed and go back to the gate.