Honestly i dont think there should be a penalty for leaving until they add solo play. There is nothing worse for some people then joining a game and seeing its basiclly a speedrun group and then being punished for leaving because you absolutely detest that kind of play. People shouldn’t have to sit through an entire level of the polar opisite of their own playstyles if they dont want to.
If they wana try to endure it…fine thats cool but if they wana say f**k it and leave they should have that option too.
Goes the other way too if someone joins a group that is slow and steadying it and they just wana blitz through as fast as possible and the rest of the team is “plodding” along and doing things at their own pace. I immagine from that end it would be equally infuriating. Add on a penalty for leaving to that…no.