What if the average daily score of a server was over 1.5X the combined score of the other two triggered the “underdog” servers to be allies for the next day (unable to fight or hurt each other but only the dominant realm?).
That might help in blowout situations which you currently have in the Seasons which makes the game less fun for all three servers.
The more tug of war the game is the better even if that requires 2 v 1. Give a bonus for the server that most often has to take on two enemies in a season if you must, but this at least makes the season have some tension versus the inevitable.