This issue is quite simple. Compared to the latest experimental snapshot, the terrain generation is a less extreme and hilly throughout certain areas in 21w37a. This is especially noticeable with the new jagged peak generation, which experienced drastic decreases in size and altitude as well as less cohesive placement. To an extent this also applies to the caves, which somewhat changed in orientation and no longer form any size-able entrances or extreme interactions with the surface. Note that this issue is valid as hkniberg stated that no changes to world generation were made intentionally, but are rather outcomes of changes to the underlying tech to allow for the porting of these features to regular snapshots. He also tweeted out asking the community to report such mismatches and downgrades in the bug tracker in order to help them get the terrain to match Experimental Snapshot 7 as closely as possible.

How to reproduce: Open up a world on Experimental Snapshot 7. Copy the seed and load it up on 21w37a, then explore and compare the differences.

Expected Results: Terrain in 21w37a should fundamentally match Experimental Snapshot 7 terrain, with few less noticeable exceptions.

Actual results: Terrain is highly nerfed in terms of elevation and jaggedness throughout various locations.

DISCLAIMER: None of the images of terrain generation present here have been found or created by me. They are from Twitter accounts who tested the snapshots and publicly shared what they found. ALL CREDIT GOES TO THEM. Please also feel free to test for yourself and share your findings on this issue. Images can really help.