As you noted pre-Ryzen they just didn't have the FCF to persue this kind of R&D. Ryzen was a bet the farm situation, if you are already betting the farm on one thing it's highly inadvisable to try do it on two things at the same time.
Nvidia benefits greatly from not having a split focus. They make GPUs, this is all. AMD needs to divide their efforts between staying ahead of Intel now that they have finally won themselves a lead which is no mean feat given how hard Intel has been chasing them down -and- putting out reasonable gaming GPUs -and- trying to come up with their first home-run datacenter GPU product which just hasn't happened yet.
I just don't see how they could have possibly had the money to try beat Nvidia over the last 5-6 years.