Overwatch does it, why can't you?
Brigitte is unplayable in Ranked at the current moment in Overwatch, as far as I can see on XBOX, (PC might be different).
But it's harming peoples gameplay and ranking going against Kai'Sa players who've played maybe 2-3 games as her.
I suggest just disabling new champions for a period of time. Either that, or new champions should require you to get to mastery 5 with them before heading to Ranked. Something to stop this blatant trolling .-.
And I'll even make this a suggestion for reworked champions as well. Cause new Irelia will not be like old Irelia, players won't have the same understanding of her kit.