I think a lot of the disappointment with this one comes from the fact they've just come off of their best event, gained some momentum and a few new eyes, and followed up with this. Obviously they can't all be Saitama Super Arena level events but this card is still a little discouraging for those of us who want to see Rizin do well.
Fans outside of Japan probably make up a miniscule portion of Rizin's income but Rizin 20's rave reviews had a few new fans checking it out and liking it. This card could turn out to be great for all we know but on paper it's not really something you can turn to a new fan with and say "Hey, this next one is worth getting excited about, too." Seems like a missed opportunity from a western fan's perspective.
Maybe they should have a different naming format for these smaller shows, like PRIDE did with Bushido. It stops the brand of the main numbered events from being tarnished by weak looking in-between cards. Bushido even managed to become an attraction all of its own in time.