[dagw]

if there's no objective measure

There are lots of objective ways to compare grinders and espresso machines. With grinders you have obvious ones like speed, but also consistency (does every run give you the same size particles) and particle size distribution (are all the particles more or less the same size). With espresso machines the big ones are temperature and pressure stability, both within a single shot and also shot to shot. All of these things can measurably affect the end result of the coffee you make. That isn't to say that there isn't also a lot pseudoscience and snobbishness also in coffee, or the diminishing returns don't kick in quite quickly.

All of this is ignoring things like design and ergonomics that many people also value. If I'm going to have a large machine that I use every day taking up counter space in my kitchen then I might be willing to pay a bit extra just for it to be pleasing to look at and enjoyable to use, even if those things cannot be detected in a blind tasting of the resulting coffee.