While I stand by the fact Luigi was denied a proper character arc, at the same time it is interesting that Luigi and Bowser were kinda two sides of the same coin leading up to the end of their friendship.
Bowser– not wanting to rock the boat after being so recently reunited with his son- fails to properly put his foot down when it came to defending The Mario Bros. Similarly, he caves easily and immediately to Junior’s perspective when he determines Mario and Luigi’s friendship was just a manipulation tactic, which all sounds awfully familiar…
The big difference is that Bowser ended up in this position by undergoing an arc– learning to be selfless, but dedicating that selflessness to his long-neglected son, who just so happens to want to go on an intergalactic mass-murder spree. Meanwhile, Luigi’s prioritized Mario for years now. Heck, Luigi subtly informed Bowser of this when they parted ways at the Honeyhive Galaxy.
In the end, while Luigi and Bowser no doubt genuinely liked each other, they are two different flavors of insecure, and I don’t think either of them were going to be confident enough to stand up for each other in a way that allowed their friendship to last long-term.
