I believe this is a bug, as I've noticed this on survival worlds and many others have as well but I haven't seen any bug reports about this.

I did this via a server using world edit.

I used the same coordinates each time and the same numbers each time,

Seed: -6798331664095837875

Test #1:

Coordinates: 224 71 -15

Command: //replacenear 100 diamond_ore air

1.16.5 Result: 502 Diamond Ore within 100 Blocks

1.17 Result: 450 Diamond Ore within 100 Blocks

Test #2:

Coordinates: 1000 64 1000

Command: //replacenear 200 diamond_ore air

1.16.5 Result: 2,153 Diamond Ore within 200 Blocks

1.17 Result: 1,803 Diamond Ore within 200 Blocks

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I'm not sure if it is meant to be less common now in 1.17 or if it was due to the first few snapshots being what is now considered 1.18 - Please let me know.