>>108761998The point is that there are a ton of thematic references that explicitly refer to showbiz and don't make sense under any other interpretation of the films. Like his duet with Lady Gaga is all about showbiz. Joker 2 even has them perform "That's Entertainment!", a song whose lyrics are explicitly about showbiz and that is heavily associated with MGM.
https://en.wikipedia.org/wiki/That%27s_Entertainment!_(song)