Again: peak draw, when on.
I'm not arguing that this system is particularly efficient, only that you don't want to add 750W for the PSU to the draw.
I've not specced out low-power systems myself. I doubt you could get 40 hyperthreads running way below this, though there are definitely some low-power systems which might have a total budget below 50W. Reddit's HomeLabPorn may have some more useful guidance: https://old.reddit.com/r/HomeLabPorn/
(Not my area of expertise, I've never really stayed current in HW. Though I'm aware power/thermal budget has been a major focus, both mobile and server, for the past decade or so.)
I specifically mention the L3 cache size because, while not being substantial, a large cache can get you 10 to 20% improved performance due less CPU stalling from cache misses. For comparison, the Xeon in question has 25MB L3, so we'd be looking at 50MB cache, split in two dies (so it doesn't quite work as a whole block of 50mb cache).
greatjack613 also mentioned the fact that an AMD Zen 3900x matches the multicore performance (and has better single core perf) for a fraction of the TDP, see https://news.ycombinator.com/item?id=20687932.
All in all that was the general idea: yes, you can get a used server for a good price, but we shouldn't forget the efficiency aspect of it, compared to new hardware.