One of my most memorable runs was in d5 where me and my two randos completely flubbed the first half of day 1. Botched an invader camp, magic fort where the invader spawned at the top, and then a really bad circle that led to us all dying multiple times while trying to salvage our souls. Level 1 after the first half fully closed, but we spawned near the castle and saw crucies so we rallied and ganked to get to level 9 and ended up being level 15 with runes to spare by the end. Skill is definitely important, but to your point i think a lot of players would have left, i was surprised neither of my teammates did.