https://screenrant.com/sitcom-supporting-characters-more-interesting-leads/

These supporting characters from sitcoms may have started with a minor presence, but they are ultimately more interesting than the leads.

Mike Hannigan in Friends was an interesting character, but to say that he was more interesting than the others is exaggerated.

Other cases: it was an ensemble cast, but the brightest star in Frasier should've been the titular character. Niles imho outshined him and the audience was mostly attached to him.
Same for Darlene in Roseanne, who became the center and the heart of the series at one point. Everything interesting was revolving around her.

Then again, it is baffling how Fonzie from Happy Days, Steve Urkel from Family Matters, and the same Frasier in Cheers were left out.