Agreed, it's a much better choice. I actually converted my entire image library to
Some examples: 4.5 MB JPG -> 109 KB webp 3.66 MB JPG -> 272 KB webp 3.36 MB JPG -> 371 KB webp
It would help to know mor about your experiment. I can get quite big size improvements here by recompressing my camera's (Canon EOS) Jpeg files to... Jpeg! And with no visible quality difference either. They go from 6.7MB for the Canon file, to 3.1MB for quality 90 in imagemagick, 1.7MB for 75 and 1.4MB for 65. And ni your experiment the WebP quality scale may not exactly match the Jpeg one which makes comparisons even harder.