Playing recently I cant help but notice that iron ore become super rare, to the point that i obtained 4-5 times as much copper. Iron ore is not generating in the mountains like it suppose to judging from graph of ore generation you have officially provided. I have seen no emeralds either.
I agree with Karol, 4-6+ times more copper than iron after running around massive tunnels and caves while trying to speed run on about 10 different worlds. It's almost to the point that you can't find enough iron to replace pickaxes that you break trying to find iron. Not a lot of iron either is visible in the tunnels and caves - unlike copper. It doesn't seem to make sense to me. There was an earlier snapshot with this problem... I wonder if the problem was accidentally reverted again in this snapshot.