The fourth season of the Ascendance of a Bookworm anime, produced by WIT Studio, premiered on April 4 this year, though to an unexpectedly rocky start. The long-running series was faced with serious backlash after the reveal of the animated opening sequence, which viewers suspected featured AI-generated assets. In response to the criticism, WIT Studio posted an official announcement on April 10, in which it states that upon investigation into the opening’s production process, it confirmed that generative AI was involved. Consequently, the opening sequence recently published on YouTube has been removed from the platform. ……



You said “almost no anime”. 20 examples is already quite a lot and not exhaustive, some of them being pretty big names. That sounds pretty prevalent to me, even if it’s not the vast majority.
Oh that I totally agree with. I wouldn’t even call it a sin.
I think there’s just miscommunication about numbers here… if there are thousands if not tens of thousands of shows, I don’t consider 100 to be more than a drop in the bucket, let alone 20, and I don’t really care how “big name” a show is.
And again, I was saying all this is the context of OP’s “greatest sin in of anime”. Do I expect there to be more shows in the future that use this technique? Sure, but barring an art style fad for a year or two, I expect them to be few and far between. It just is not a technique that is at all indicative of what “anime” is or has been.