I actually had the 4mil design for a while already, can't remember since when. Merch was up and down coz my team's performance wasn't that consistent too, but it did go up considerably towards end of last season and into playoffs. Oddly it fell a lot after the new season began.
Team Sales $ 67 666
Player Jersey Sales $ 77 985
Homegrown & Locals $ 31 504
Arena Sponsorships $ 23 809
Merchandise Store $ 23 750
Seems that Sponsorships are indeed based on arena design!
I maxed out all my infrastructure too. Had been saving up over a few seasons and eventually spent all on upgrading. Seems that Merchandise Store pays for itself (the 15k maintenance) and a little more each week, and arena design will also take a long time to breakeven. Too lazy to do the math now haha to see how longterm it has to be for them to make sense.