Just have a "elo" room where people of certain rank can enter. new people have to do 1 vs 1 if they want to progress.
I play for elo team games. I don't play 1v1, if elo is removed from teamgames then there is no point in me playing because I like playing with others to increase my elo. I don't like playing 1 vs 1.
You could disable Elo gain when the teams get bigger. so smurfs have a lesser impact. if anything bring back small games room. any games with more then 5 people on each side, elo is disabled automatically. bring in a command to re-enable it but it has to be by majority vote. If anyone plays those games then it was their choice and their risk.
Lastly make it harder for people to smurf.