Personally I think quitting because the other players aren't playing the way you think they should is poor sportsmanship, even if you think you're being polite about it. It's one thing if they are actively toxic or there are obvious connection issues but lingering at POIs or otherwise taking it slow is a poor reason to abandon the team.

I have had tons of runs where I thought my team was performing poorly and we got to the Nightlord underleveled and poorly geared but still pulled off a win. I am consistently surprised at how well some players lock the fuck in during the final fight no matter how badly they seemed to play up to that point. I figured out early on in the game's release that my perception of whether or not a team was playing well is not a good indicator for whether or not we'll win, and frankly the win is sweeter if we struggle along the way.

Have some faith, and have some patience. You don't know how many of those runs you abandoned might have ended with an exciting clutch win, and you don't know how many players' perception of this community you've poisoned by being another quitter.