This one just shows you don't respect games as an artform and also secondarily that you don't know what you're talking about. Treating gameplay as a direct parallel to cinematography in film just does not work at all. Gameplay is much more akin to prose than it is to cinematography, in the sense that both gameplay and prose serve directly to inform and convey the experience of the art itself. Good prose can't save a book with bad structure, but a book absolutely requires good prose in order to be a good book.
Even within that comparison, though, gameplay is distinct, because crafting very mechanically tight and "good feeling" (for lack of a better term) gameplay can be the central point of a game in a way that really good prose just can't do for a book (see a game like n++ for an example of what I mean.) This is because games are fundamentally just more tactile than film or books, and in that regard a more apt example is the visual arts. You wouldn't argue a painting needs good writing to be a good painting, right? No, because you'd be completely missing the point of painting as an artform. The direct communication of an idea to the viewer through visuals is potent enough to be an artform in itself. n++ is much more like Untitled (Red) than it is like Ulysses (and much more similar to those than Citizen Kane) but it's also nothing like any of those things because fundamentally it's its own thing, which is a video game.
Ultimately, equating "gameplay can be the centerpiece" to "not all games have to be art" completely misses why games are unique as an artform and, honestly, just reads as thinking games can only be vessels for art rather than art themselves (which, I mean, that's what you directly state when you call a game a sandwich with a filling. What an awful metaphor that you constructed your piece around.) It's a disrespect to the medium. If you just want games that are books or movies, good news! Books and movies already exist. Games are their own thing and your thinking of what makes good movies simply can't be mapped to them the way you want it to. This kind of thinking is how we end up with more God of War reboots and TLoUs than n++es and Dooms and VVVVVVs and Ape Outs and Yume Nikkis and Hotline Miamis and things that just fundamentally take more advantage of what makes games unique.
tl;dr you thought that it was developers that didn't understand that games are art because they can be like movies, but it was actually you that didn't understand games are art in a way that making them like movies betrays! ha HA!