It was already much rarer than Iron, Coal and redstone, it didn't need a nerf. This takes the fun out of strip mining and makes it even more of a tedious task than it was before. Because of this friends on my world are going to need to rethink their strategies and also refrain from using diamond blocks for any sort of decoration to save resources. Diamond ore takes too long to get to, and by the time you do find it you're already bored with mining, if you didn't reach boredom before finding it. My biggest misgivings against 1.17 isn't the terrain generation though, it's the ore distribution, it's terrible. I know shovels need some kind of a purpose, but they already did before Caves and Cliffs and it was done for more reasons than simply altering terrain, you used it to make water holes for farmlands, you used it to clear away sand, dirt and gravel in mines faster than with any other tool, and you used it to get flint 100% of the time using fortune 3 from gravel. Now hills are even more of a pain in the rear to flatten, given that they've also been enlarged. Something along the lines of a mixed amplified and large biomes type of world if you will. They should've made the terrain generation more varied, than simply just enlarging every mountain in the game. The mountains look cool and realistic though.

I think 1.18 is the worst update Minecraft has ever had! The terrain is too hilly and there are barely any flat areas! The new caves are making it impossible to find diamonds at y11 like I'm used to doing! The only thing I like is that emerald is more common as it generates sometimes on the sides of mountains.

Minecraft version 1.18