There are plenty of things in life that aren't your fault but still are your responsibility. Banning people from ranked until the system is sure they have a stable connection and then restricting them again when they start disconnecting should be standard.
I used to tack people out of curiosity when I was trying to diversify my champion pool, playing 2-3 champions on an account until a certain elo, but I gave up after ~6 months seeing the same people still have daily/weekly ranked leaves in their history.
And while it was true that at the end of the day, on a lot of accounts and over a lot of games I had less leavers in my team, I had accounts with bad luck in terms of leavers. Even if I was better at the champions I played, it took me 10-15% more games to get to the same elo as an account with good leaver luck even if I played worse myself.
Everyone trying to justify it being "ok" because if you don't leave the enemy team will have more leavers on average has to understand that it's over a HUGE number of games and bad luck can screw you. That's also why the correct way to climb high in ranked is to play an account for 3/4 of a season and then use a new one to climb with high win-rate over a few games when you get used to the season.