I wonder if there were NUMA effects at play since the Intel server was dual-socket and the EPYC was not. It's not entirely surprising that a CPU-heavy workload reading from filesystem cache (i.e. memory) could cause a substantial amount of nonlocal reads that the single-socket server wouldn't have to deal with.

That said, that's just the first thing that popped into my head to explain the result. Either way, the results here are extremely encouraging!