I had a few FX cores (and I keep yet stored). The early cheap 4 cores and the latter generation 8 cores (FX 8370E). And I can say that if you run code that scales well with multiple CPUs, it excels at it ( I can share a n-problem simalutor that I used as benchmark back in the day) Even, they aged far better than some Intel cpus of the time, because they had 8 cores.

FX cores had his issues. But one, was the AMD bet too early, and too hard that the future was to have a high number of cores.

Problem was that even for multithreaded workloads the "8 core" FX-8150 did not always win against 4 hyperthreaded Intel cores. That is pretty apparent from e.g. the benchmarks here: https://www.phoronix.com/review/intel_corei7_3770k

You can easily see the multithreaded workloads there because you have the six core 3960X as comparison too.