1.17, 1.17.1 Pre-release 1
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,
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
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
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.