It sounds to me like it was too small to make any real difference except in very specific scenarios and a larger one would have been too expensive to implement compared to the benefit.

That being said, some workloads will see a small regression, however AMD has made some small performance improvements since launch.

They should have just made it a BIOS option for Zen 4. The fact they do not appear to have done so does indicate the possibility of a bug or security issue.