I think there should be a few small changes in One for All
The first is how the champion is picked. I feel like it should really be a lottery rather than majority. What i mean by this is say you have a 4 man premade, they will all pick the same champ meaning the solo player is stuck with whatever they choose. I think it should be an 80% chance of their champ being picked instead of majority rules. Obviously if its 5 for one champ then its 100% but unless everyone chooses that champ there should be a chance for the other champ.
The second is a more recent issue. In OFA you can be ANY champ in the game including ones you don't own. This is the best part about OFA imo but if you don't own the champion you can't get any keys. Seeing as rotating game que has a higher drop rate for keys (or atleast I think they do) i think you should change it for this one mode rito gaems