There is a massive performance regression in the snapshots 21w37a and 21w38a, which does not happen on 1.17.1.
Depending on what you are doing in-game frametimes can be easily 30 to 40 ms more than the worst case on 1.17.1, resulting in about half the average FPS during normal gameplay compared to 1.17.1 on my setup.
GPU utilization is about the same (at max ~ 35%) in all tested versions.
I was not able to test each version on the exact same map due to seed weirdness, so 1.17.1 is in a different spot, but one that should be even more GPU heavy than the scene in the snapshots, yet performs way better.
I've noticed a slight drop in performance myself since the last snapshot, and even the experimental snapshots. The experimental snaps ran surprisingly well for me at a higher than usual render distance even, and so did the first official snapshot. But this version, 21w38a, seems to be worse, probably because of the new simulation distance setting being added. I'm sure it'll work itself out as they work on it.