If Champs Are Being Permabanned..
You should probably look into why they are being permabanned instead of finding ways to keep them from being permabanned.
If they have extremely high ban rates there's a reason why, whether it be frustration in their kits/playrates or something genuinely unhealthy.
And if you are going to create ways for these champions to see more play then you really have to pay attention to why they were being permabanned in the first place..