AV1 has issues with film grain. There are things you can do. Let me admit however that one movie that I have not encoded as AV1 is a restored version of the original Star Wars. And film grain is a contributor to that.

Another thing about film grain though is that it is often artificially added after as you say. With AV1, you can often get amazing compression that removes the grain as a side-effect and then just add it back yourself. To each their own how they feel about this approach.

I also agree that H.264 can be more transparent. However, that is at massive file sizes. Others may have the space for that but I do not… Perhaps I do mot have the eyes for it either. I am not extracting and comparing single frames. To me, the AV1 files that I have look better at the size that I am archiving than they would using any other codec.

I use the fact that massive bit rate H.264 looks great to my advantage as that is what my AV1 is being transcoded into when I watch it most of the time.

Some content compresses better than others. Sometimes I get massive size reductions with AV1 at what looks like great quality to me. Other times, it struggles to beat H.265 or even H.264 at similar quality. It is pretty rare that I do not choose AV1 though.

I often use Netflix VMAF to get an idea of target compression. It is not perfect though. You have to verify visually. Saves time trialing different parameters though.

I should say that the audio codec is another big factor. I typically pair AV1 with Opus audio and the size reductions there are amazing even at quality levels that are transparent to me.

If AV2 offers better quality at the same size, or similar quality at smaller sizes, I will likely switch to it long before having hardware that can play it natively.