Well but you cannot have a 5-10 times smaller WebP at a quality comparable to JPEG. If low quality is good enough for you, then you can get maybe a 10-20% savin

Well but you cannot have a 5-10 times smaller WebP at a quality comparable to JPEG. If low quality is good enough for you, then you can get maybe a 10-20% saving compared to JPEG (not 80-90% as you are claiming, that is ridiculous). At higher quality, WebP does not really save anything compared to JPEG. At camera quality: WebP cannot even do that, its lossy mode has a maximum quality that is well below the kind of visually lossless encoding cameras use.