In my opinion the worst and most distinguishable downside of webp is the forced 4:2:0 chroma subsampling. On many images with bright colors you can clearly see the color and brightness loss without an educated eye.
On comparison [1] you can clearly see that the top right balloon has lost its vibrant red color. On comparison [2] the bright blue neon art on the center has lost its brightness.
Not to stir yet stir another debate but yeah, definitely not able to perceive the difference in either of the examples you linked. It would be helpful if that site let you drag the vertical comparison bar at least. On an iPhone 14 display.
I can see it in the second link setting webp to small in the orange reflections above the rightmost outside needle tree htms. ... oh, you cant drag it? ...
On comparison [1] you can clearly see that the top right balloon has lost its vibrant red color. On comparison [2] the bright blue neon art on the center has lost its brightness.
[1] https://storage.googleapis.com/demos.webmproject.org/webp/cm...
[2] https://storage.googleapis.com/demos.webmproject.org/webp/cm...