It's a big deal :(

JPEG artifacts are literally a meme, normal people are aware of this stuff.

I hold the extremist view that had we decided to use .png for lossless webps, it would have been an overall net gain - in people's minds "png" maps roughly to "whoever last touched this image didn't do anything evil to it" - very few people care how the data is actually encoded.

I mean we are already dealing with that nowadays. Many PNGs are either JPEG in a different package or straight up lossy compressed. Unfotunately extensions have never been safe for judge