I think this is the way to go as well. I just simmed to 2022 while editing SP potential -15 for each draft class. League-wide ERA and batting averages look great, but there's a 'realism' problem I don't like.
When the SP potential is nerfed to this degree, you will almost never see any SP good enough to make a rotation until they are about 28 years old. Overall ratings were outstanding, and almost exactly matched the roster that I started with, but you never get any younger players cracking the rotation.
Another thing to look out for is the fringe SP 70-75. They will just hang in that range until they hit their declining age. I plan on manually regressing some of these guys each year depending on their stats. Without doing so, they just kind of clog up the 5th/6th starter spots instead of going away as they tend to in real life.