Overall I like this concept, normally I balk at adding complexity but by the time a player progresses to Survival mode it shouldn't be a stretch.
Not sure if the voluntary league lock ads a lot of benefit though. Breaking through to a new league a few times a season throws in a few hits of dopamine, which is very much good for the game. Could players choose their starting league, but be allowed to move up and down? The cooldown would be based on the league the card was in when it was beaten.