In Depth Worldbuilding

Several other games that are multiplayer competitive games have extensive world building that adds a layer of depth and interaction with the players. The Finals and League of Legends both frame their gameplay within a larger world building context, which I think adds a layer of immersion that I would love to see in Rematch. You have already started on the idea of it with the environmental energy inspired stadiums; in your art design document you imagine a sci fi world that is hopeful rather than dystopian. Here are some ideas to continue to expand upon what is already in the game.

Stadium Levels:
If you abstract the players rank to be similar to what league they are in, similar to real life promotion and relegation of clubs, if the stadiums got bigger the further you advanced it would add to the excitement of going up a league, and be an exciting reward for reaching elite.

Season Pass Narrative:
Instead of each season having a visual theme, incorporating a narrative theme would help ground some of the ideas. Similar to real world marketing, having a brand identity for Torkal would make players excited to receive their items, and flesh out the world of Rematch. For example, maybe Torkal wants to sponser the best players in the world, but are getting out manuvered by another brands. And maybe Torkal isn't just a clothing brand, but a coal company as well, so their designs are brutalist and industrial, trying to steal the spotlight from the green energy focused Rematch organizers.

World Specific Events:
Having challenges based on in game world building would help immersion as well. Maybe a football club is looking for a new playmaker, so if you get a certain amount of assists by the end of a period you get a special title or banner.
I'm not a game designer, so these are not the strongest suggestions. But the world building is beautiful and exciting, but desperately leaves me wanting more from it, and more ways to interact with the world.