It shouldn't be completely impossible to retain the League as an institution
We all know that the physical League of Legends was removed from the lore because it forced every champion to have a reason for joining the League.
But there's no reason to scrap the concept entirely. Without the League of Legends, the lore of the champions is literally just a random story with nothing to back it up, which is why a lot of people didn't like the change.
The League of Legends could be retained as a method of resolving conflicts on a small, controlled scale, without requiring that champions live on-site at the Institute of War. Instead, when two nations have a conflict they would simply choose representatives to go fight in the League, but at any other time the champions can just run around and do what they want. This makes the League actually relevant to the lore and answers the question of why you have these 10 people randomly fighting on a magical field that respawns you.
I feel like this is a nice compromise. Thoughts?