There's really no explanation for why EPYC "Naples" was so bad other than AMD did not internally understand the performance of realistic large-scale programs. I mean even if they had taken anything off the shelf, for free, like MySQL, they could have determined at some point before mass production that their CPU, in fact, sucked. But they shipped it and prospective customers rejected it.

Don't discount how a weak organization can make poor decisions even when all necessary information seems to be readily available.