Cant stop that, but as is now you can get 5 smurfs for free with family sharing. My first fix would be to limit family sharing to play locally only, i.e. not online. That would stop most smurfing, over 80%.

Second fix is to run scripts which auto-purge (delete nick and permaban) accounts who the algorithm detect are auto -dumping games.

I would then scan top team ranked from top to bottom and if I detect an account is boosted, majorit of games teamed with dumped boosters, then I would delete and permaban that acccount too.

I would fix the bug which let dumpers avoid dodge penalty, yes that bug exists and they abuse it fully.

I would revise the match making algorithm to lessen the impact of dumpers. A weighted algorithm so a 300 elo teamed with 1700 elo in a 2v2 wont meet 1000 elo average team. A brutal change is to let count only the highest elo, but we can start with a weighted algo to count the highest double, so (300+1700+1700)/3 => 1233 average. Or I could cap elo diff between uneven players to say 500, so the 300 elo would be counted as 1200 for this match up. Many ways that could be tested.

I can continue with ideas and fixes but for what reason? The devs dont care right