This is a major improvement. It's better than WebP by a bigger margin than WebP was better than JPEG. Lossy WebP couldn't even match JPEG in some aspects, like

This is a major improvement. It's better than WebP by a bigger margin than WebP was better than JPEG. Lossy WebP couldn't even match JPEG in some aspects, like full-resolution color (4:2:0 only, not even full 8-bit depth). In terms of quality or features AVIF doesn't have such "buts". It can support HDR and high depth we're likely to want in the near future. AV1 has palette blocks, so it's no longer all-or-nothing choice of lossy vs lossless formats. I am worried that the AVIF spec is complex (like HEIF, it's a bag of image-related features, more like a PowerPoint file than an image), but probably only commonly-used features will survive out of it. Early JPEG also used to have many more modes than are usable today. If you like questionable hacks, you can use AV1 codec today in Firefox and Chrome by embedding <video> element with a 1-frame AV1 "video".