I'm completely convinced that at least 90% of the people complaining about chapter 5 have not played the game
I have not seen any comments from the people bitching about the "lack of plot progression" about quite literally anything in the game except plot. Not a single comment about how fun the platformer mode was, or how cool the music was, or anything about the subtler developments of the lore in character and thematic development.
I have not seen them say anything about anything except for "wah not enough plot" and "ooh weird route" for that matter. And like, my question is, have they actually played the game?? If you played the chapter you would see how amazingly FUN it was. Sure, we didn't get much information about the knight or overall game lore, but we got so much other stuff.
Even ignoring gameplay, just talking about lore, we got to see Asgore's behaviours which led to the divorce. We got the reveal that Ralsei can use fire magic. We got so much character development from Ralsei, Susie, and indirectly Kris.
Chapter 5 was a good chapter even if it didn't advance the main story that much.