As a fan of MTM since age 0, we will have to agree to disagree there, lol.
I do agree that MTM is a very different tone from TMS. It's more about sentimentality than cynical show biz humor. I just don't see much resemblance between TMS and MMW (or TM).
In TMS they all kinda know the show is bad, but they're proud of it anyway. It's the embodiment of the "What, and give up show business?!" joke.
In MMW, the joke is on them not knowing how unpopular they there or even why. That's not funny, that's embarrassing.
And frankly, I don't want to see a meta Muppets movie. In the original three films, they put themselves into artificial, dramatized situations. In TMM, they're playing fictionalized versions of their earlier selves. In GMC, they're playing completely fictional characters in an old fashioned Caper heist. In MTM, they're recent college graduates. It all hearkened back to the old days when Laurel & Hardy or the Marx Brothers were always playing different characters in different situations, just with the same personalities. But you didn't see a Laurel & Hardy movie where they sat around wondering if they're popular or not.