This is something which didn't come through in my original post, but I feel one of the major problems here is that people are trying to compare video games to other mediums such as theatre, movies, and books. In other words, video games are an art form which is different enough that direct comparisons to other art forms may be misleading. Now I realize that we are talking about the general quality of plot in games, and not the wider debate regarding whether video games constitute art. That said, imagine the complaint that music is not art because it lacks a proper plot. Video games have aspects of other mediums, but the interactive nature of games means that they will never really be directly comparable.
For example, in film school you might study aspects of film which are somewhat oblique to the quality of the actual storytelling in the film. Such as: cinematography, and the framing of characters in the shot. Video games have analogous things, such as level design, game design, etc. A famous example is how the first level of Super Mario Bros. teaches you that mushrooms are beneficial, by making the player's first interaction with one mostly unavoidable. Modern games have more complex game designs, and of course these designs represent a complex communication between the game creators and the players. A lot of nuance an information is conveyed this way, and it can potentially amount to art. Much like the art of cinematography cannot exist in books, the art of game design cannot exist in other mediums.
Video games can also teach you things which movies and books cannot, (at least potentially) and this can be performed via game design. For example, when I was a child, people would exclaim "life's not a video game!" I heard this quite a bit, and I believe most people meant: the things you do have consequences, and you won't get very many second chances. Now this is frankly not really correct. Yes, the things you do have consequences, but almost everyone gets multiple second chances throughout their life. For example, if I fail at one task in a workplace, I usually get multiple chances to improve and correct my error. Even if I fail overall at a job, I will likely have future chances to prove myself at other jobs. Some mistakes can be fatal, of course, but for most of the actions I take, I can plan on success by trial and error, repetition, and iteration. In other words, exactly like a video game. Interestingly, it was video games which first taught me this. I had a friend who by all accounts was objectively not as talented at video games than I was. We'd play together, and I'd best him at nearly everything we touched. However one day he wanted to take on a challenge in a game which I felt was above my skill level. I was certain he'd never be able to succeed, because I was certain I could never succeed. But, he had something I didn't at the time: persistence. He kept trying and failing, and trying again. He never became discouraged or emotionally frustrated, and slowly he iterated on his failure and eventually succeeded. (To be clear here, when I say "iterate on failure," I simply mean to attempt a task, fail at it, and attempt it slightly better the next time.) I learned a very important lesson that day, and have been re-learning it ever since: part of success is persistence, and things which seem impossible are often simply daunting. Later in life, Dark Souls and other From Software games reinforced these lessons, and of course much more importantly, I applied these lessons to my everyday life and learned not to fear failure, and to iterate on failure until it became success. I bring this up specifically because I remember years ago reading an interview with a celebrity who felt that video games could not be art. I believe it was Roger Ebert, but I'm not sure. In either case, the argument was made that art teaches you something, something about human nature, something about being a person. It's possible I'm misremembering the argument, (I can't find it online) but my point is the same. Video games taught me something about being a person which other mediums failed to teach me.