I use Metallurgy though
Coal is super duper common forever but you need a forgetbuttload of it so that's okay
And everything spawns at any depth, I've found surface exposed Diamonds before but they're actually rarer than normal to compensate for spawning at any depth or so I've observed (aside from the two I found there I mined for about three hours in a really big cave system - had a full inventory of nothing but ore, a crafting bench and sticks for tools, and no more diamonds)
Then again Diamonds in Metallurgy aren't too important, since Steel tools are on par with Diamond and just take some Iron and Manganese to make. (Crush iron and manganese ores into powders, craft and smelt - Manganese is pretty common too)