Here's what you can expect with just exploration surface mining in areas below y=0 for a few hours.
(mostly surface mining, a lot of the deepslate pictured is from mining out an area for the beacon at bedrock)
(I skipped a lot of plain iron and Redstone, went mostly for Deepslate variants)(The Netherite Pickaxe is Unbreaking 3, so that might give you a better gauge for how much mining there was)
(P.S. Efficiency V Netherite Pick + Haste II does not insta-break deepslate)
Source: https://www.reddit.com/r/Minecraft/comments/lt9lod/mining_below_y0_snapshot_21w08b/
