Using the Mac Mini form factor and a comparable Ryzen mini PC to judge the processors' suitability as mobile chips is certainly less than ideal, but it's not as worthless as you seem to be implying. In particular, this kind of comparison makes it far easier to get a more apples-to-apples comparison of the chips themselves, without other system design decisions as serious confounding variables. You won't find AMD's top mobile chip in any form factor that remotely resembles a MacBook Air, for example. And when trying to compare a MacBook Air against a Ryzen notebook that's 3-4x as thick, you wouldn't be able to make as strong a conclusion that it's the chip itself and not merely the heatsink responsible when the Ryzen does deliver higher performance.