After simming several more seasons I noticed it did start to even out a little once all the modern day pitching prospects started to regress / retire.
I don't have any solid numbers for you but when I skimmed over the pitching rotations I noticed that the majority of pitchers we're throwing high 3s / low 4s (4.00 ERA's we're more common).
This could be an effect of high number of potent hitting prospects generated over time as well as the CPU's poor handling of pitching rotations, prioritizing hitting over fielding ability etc...
On another note: The game generates way too many skinny midget prospects. I don't want the 5'7" 160 pounder even if he does have 98 potential. CPU will swoop him up though.