On Zen 4, running UCLK and FCLK at the same frequency provides no memory latency reduction.

This is incorrect, it’s a very substantial latency step reduction and offers ideal performance in certain workloads. 8000/2000/2000 tests lower latency than 8000/2000/2200 and around 4ns lower than 8000/2000/2033.

There’s even a flag in ryzen master which shows if uclk=fclk sync mode is active or not.

Phoenix 2 has zen4c and is releasing on AM5

AGESA 1080 included fclk improvements which increased the max stable FCLK for many users. On my 7950x3d the maximum stable FCLK went from 2133 to 2200.