the claim here is that centrifuges face technical hurdles that are worse than diffusion pipes
As you say, looking at it as a physicist ( deducing from first principle) it is hard to support that claim.
FWIW here are my thoughts
Unlike involvement of laser (or similar techniques); where you selectively ionize (or chemically change) just one isotope and thus, later can use a simpler method to extract one isotope, both of these method, as you say, use “mechanical technologies” and one would think that centrifuge technology can not be worse than diffusion. Although, once one has invested a lot of money and effort (Like US did for diffusion, and Europe/SU did for centrifuge) in setting up plants etc, “other” technology would be “worse” in practical sense.
One piece of data, at present, I am fairly sure, that there is only one commercial diffusion plant in US. (Paducah, KY) The diffusion plant in Piketon, Ohio (which produced HEU for bulk of US bombs in 50's-60s) closed down. Interestingly there is a centrifuge plant
under construction in Piketon now.
I would like to know more too.
Added later: American Centirfuge Link