What I mean is that did doubling down if you will on the issue-oriented, very special episode or afterschool special format hurt its popularity in the long run? Think about it this way, its sister show, The Facts of Life (https://www.sitcomsonline.com/boards/archive/index.php/t-415789.html) in comparison, became a decidedly a lighter sitcom more comedy focused show around Season 6 in 1985 or so.

Diff'rent Strokes meanwhile, by its final season, was doing episodes (https://www.reddit.com/r/television/comments/itj7xl/why_did_different_strokes_had_so_many_dark/) such as Sam being kidnapped and Kimberly suffering from bulimia. It was already about two seasons prior that the show did another kidnapping based episode when Arnold and Kimberly were hitchhiking. It just felt like Diff'rent Strokes really went into overkill or went overboard (https://www.tellytalk.net/threads/diff%E2%80%99rent-strokes.14607/post-401187) with these types of shows.