I was thinking an easy solution would be to scale the required dps for getting chests, based on how many people in your party are currently gathering.

It can get frustrating when you go in to farm gear, and it turns out you're stuck with a partial pre-made for gathering. Happened to my gf and I yesterday, 5 of the party were gathering, and only 1 other person was there to farm gear. We ended up just leaving because we couldn't get any chests to drop.