Chunks have no blending at all. 

I have a taken worlds from 21w38a and tried using all 5 pre-releases to blend them. None of them blended, giving harsh borders on each chunk boundary.

How to replicate: Create a world in 21w38a. Then reload the game and play in Pre-5 and fly to the edge of the loaded area. Once there you will see the chunk borders and lack of blending.