One solution to handle smurfing in rank...
It's easy, it's already partially in effect (in clash), and nearly everyone can do it.
Phone authentication.
Binding an account to a phone number would drastically reduce extra accounts from impeding on fair, ranked games.
What's that? Don't have a phone? No problem! Don't participate in ranked games. There is still drafted games, blind picks, ARAMs, URF that you can participate in.