I consider that WebP lossy was fixed to usable quality level around 2015, five years after the launch. For the first five years it had a tendency to make 4x4 pixel lego-block representations of smooth gradients and lose highly saturated colors.

8-bits per channel and YUV420 only were caused by hurrying it.

With JPEG XL we have the opposing mistake. We had a great format already in 2017, and spent 5 years more for improving it further.