From what i've seen JPEG XL always wins against AVIF in every category. What makes you say AVIF would be "objectively the best" while JPEG XL boasts better compression, more funtionality(32bit support e.g.) and faster encoding?
AVIF does better at low-bitrate scenarios ( low bits per pixel, quality is going to be poor anyway, avif can make it less poor) while JpegXL does great at higher bpp and lossless scenarios
