The opposite might be true, the better you are at utilising the CPU pipeline the less space you have to run a 2nd thread so SMT's benefits might diminish
Correct. However, Zen 5 seems to be the first major 'scaling up' that AMD has done since the original Zen, given that the core seems to be moving from dispatching 6 to 8 instructions per clock and 4 to 6 ALUs. I would expect that SMT to be excellent for low-IPC workloads to get the most out of that scaling.