It's fine to let your team rot if they're doing poorly, if they're sucking and you know that if you engage you will end up losing the fight since nobody except you does damage, maybe its best to win the game by other ways, afk farm splitpush and whatnot, its what top jarvan does best anyway aka oneshot out of position squishies, which is easier to do when not in a teamfight, 100% at some point there was a 20 iq squishy in their team going to farm a lane alone without vision, thats where you need to be, look at the wave and imagine how long does it take to build up, if it does, position yourself over the wall when someone comes to farm and there you go, free kill, pressure put because someone from their team is dead, perhaps you have time to take the tower, if not, damage it, you prolly also took 1-2 waves after doing that, pretty easy, just gotta not get caught while trying to position, which is why you also should have a sweeper btw.