Underclocking isn’t necessary for it to be more efficient, if AMD is to be believed. A higher peak power does not mean generating more heat / using more electricity to perform a given task, as long as the task can be completed proportionally faster.

But, efficiency is often a curve, and you can supposedly get crazy efficiency by limiting the TDP of Ryzen 7000, so it is an option for those who prize efficiency above maximum performance, and it would still represent an improvement over a Ryzen 5000 at the same TDP. As I said, though, we’ll need to see actual reviews.