Even nowadays, webp seems to be good specifically for its lossless mode. It seems to create files that are substantially more efficient even when compared with advanced png encoders. For comics, png should probably be used over jpeg, so webp is likely indeed an upgrade, aside from compatibility.

For photographs, jpeg has really been optimized without reducing compatibility, and also in another less compatible way (incompatible viewers can display it without erroring out, but the colors are wrong) and there's such an encoder in the JPEG XL repo.