ELO/WHR is fun to have, but I find it an approximation (due to new players, play style variability and other reasons).
Ideally everybody should have a slider what "chance" is willing to take to join a game, I would personally probably accept 35% chance of winning to play in a "smallish" game (between 6 and 12 players).
For larger game I would like to have a maximum variation to join a game, sometimes balancer puts best one + all the worse ones in a team and all the other in the other team (or milder variations of this pattern), which I find quite bad balance.