Clipshows were a necessary evil on broadcast shows, especially scifi ones that cost a lot of money. Sometimes the show would have to do a clipshow or a noticeably cheap bottle episode to save up for an expensive episode. Also, in the pre-streaming era, people couldn't just watch all the episodes in order on demand so an occasional episode summarizing what was going on was actually useful.

I liked the clip shows from Community because they showed clips from "episodes" that weren't shown. They would just reference events that we didn't see happen and show a clip of it. Idk if that counts though.

I think clip episodes are actually when the production runs out of money so they force the writers to make something very cheap. Usually at the end of a season.

There's usually a large chasm between the good episodes and the low quality of a clip episodes, rather than a gradual decline.