Squoosh does not use best-in-class codecs [1]. Lossless PNG compression is 5-15% worse on average and lossy PNG compression (color quantization) is limited to PNG-8, which is not enough to maintain image quality. Lossy JPEG compression is only tuned for 4:2:0 chroma subsampling and causes blurring of fine details because trellis quantization is guided simply by the variance in DCT domain.
[1] https://optimage.app/benchmark