I have a suggestion for a new season. It seems that you build up a variety of characters but you only get to use the different teams for wars on a consistent basis. How about a season that requires you to fight different waves with different teams. For example, the first stage would have you fighting 3 waves with 3 different teams, meaning you have to have 15 different heroes to field the teams to beat the stage. It could go up to 9 waves for the hardest levels.
Additionally, a season with a campaign like this could drop better treasures than normal; for example, perhaps it drops 3* classic heroes, or maybe the much needed rare ascension items at higher stages.
Moreover, these “waves” should be really challenging as it would be a Season 4 or 5 kind of initiative.