Google created webp and that is why they are giving it unjustified preferential treatment and has been trying to unreasonably force it down the throat of the internet.
What you’re referring to is pngquant which uses dithering/reduces colors to allow the PNG to compress to a smaller size.
So the “loss” is happening independent of the format.
https://blog.cloudflare.com/uncovering-the-hidden-webp-vulne...
FWIW webp came from the same "research group in google switzerland" that later developed jpegxl.
The funny thing is all the places where Google's own ecosystem has ignored WebP. E.g., the golang stdlib has a WebP decoder, but all of the encoders you'll find are CGo bindings to libwebp.