This mirrors my experience with Zen 2 and 3 as well. Multi-core loads result in just a few W per core and decent temperatures, while few or single core loads push per-core power into the 12-16 W region and the temperature rise/fall is basically instant (brick-wall at 10 Hz update rate, though it's unclear what filtering is applied and how the CPU derives a single temperature from its probably numerous sensors), which suggests that they're not limited by the cooler, but rather by the thermal impedance from the active area to the cooler. The core itself is really tiny (iirc around 4 mm²)...