You can adjust the speed of both, you don't have to use the default of whatever library versions you're using. My cjxl defaults to 2x more CPU than avifenc's default, but I can make it 30x more or 480x less; libaom certainly lets you waste a lot more CPU than libjxl, if that's what you want.

I don't know if anyone has published an encode time / quality comparison of the various encoders. It'd have to be recent to include this year's libaom image optimizations.