So what's this AVIF format they mention that's actually better than both?

WebP did not take off.

But will AVIF be any better?

It's based on the next-gen AV1 video codec. I've tried it out, and it's amazing.

https://netflixtechblog.com/avif-for-next-generation-image-c...

https://github.com/AOMediaCodec/libavif