Honestly, I'd recommend giving Varus a try.
He has great poke and waveclear, making him very good at stalling out enemy pushes and for sieging/poking around objectives.
If they ever try to engage a fight or misposition, his ultimate can lock them down long enough for your team to murder them. Even if they aren't very skilled, most players know to pile onto the CCed target.
You don't really need coordination. If both teams randomly group around an objective, just start poking them down. Hopefully, you will have reduced the enemy team down to about 60% HP or less by the time a fight starts, giving your team a massive advantage.