Earlier quoted context omitted.
There are a lot of things that have to go the wrong way at once to get to the point where that really matters. The first is that your working set won't fit in the processor caches and has regular cache misses into main memory -- but most of the Epyc line has 64MB of L3 cache. Then the access pattern has to be random rather than sequential, which knocks out a major class of the applications satisfying the first criter…
I don't think you really understand the architecture of the machine. EPYC looks on paper like it has a large L3 cache, but it consists of separate L3 caches per "core complex" of which there are two per die and four dies per package. So what you've actually got is a bunch of redundant 8MB caches, which is not the same thing. Because of the baroque topology, especially when you have two sockets, access to main memory…
I think you know that "total disaster" is pretty much hyperbole.