despite a loaded cast, it had no huge, bankable star giving a centerpiece performance

Ensembles aren't supposed to, neither are SHMs - the IP is the star. Mystery Men is based on background characters from Flaming Carrot comics, which was brilliant but super niche.

It has a hard time balancing a futuristic setting with contemporary 1999 America

It's a parody of 1980's/1990's comic book movies (they actually reused sets from Batman Forever). The catch is that 80's/90's SHMs are so stylistically different than 10's/20's SHMs that the parodic quality is lost. I would love a sequel/6-10 episode mini-series that takes on the MCU/DCEU.

In another universe, with some better editing and better directing, this is one of the better movies ever made.

The bummer of the project is that everyone on screen hated each other.