Using the same idea in PVP zone, wait until every player has loaded and start to play.
OR
While the player waits for the other loading the game, the elevator gates remain closed!
Or both...
I'm saying this to be equal for everyone, specially the guys who love to rush
I would find your idea insanely annoying. I don't want to wait because a random guy joined me and has a very slow loading time.. I want to do what I came to this game for, I want to play. And it's not like I finish the whole depth before the other can even begin.. 1 or 2 monsters more killed perhaps, but the heat and crowns are shared anyway so the slower player doesn't lose any of that?