almost right
Your post isn't quite right either. The heavier bullet moving slower will have more kinetic energy as well as more momentum and recoil. For every reaction there will be an equal and opposite reaction, this is the Law of Physics that applies every time you pull a trigger. The 9mm should have less recoil using a bullet in it's average weight class than a 38 Super using a bullet in it's average weight class. Use a heavier bullet and the recoil goes up respectively because the weight of the bullet goes up as does the load of powder needed to fire the heavier load. More powder and weight of bullet equal heavier recoil to the shooter because of the same Law of Physics will always apply.
You can change the bullet weight of a 9mm to a heavy one and it have more recoil than a lighter load in the 38 Super. Energy plus momentum gives you the recoil. If you use a very heavy recoil spring, the felt recoil can be lessened by the spring, but actual recoil is still going to be the same no matter what spring you use. There are a lot of different things that go into felt recoil and I am not going to touch them all here, but there are things that can be done to lessen the effect of recoil. How you hold the gun with respect to the hands and wrists being inline as well as not locking out the arms will help lessen the effect of recoil. Neither of the two guns you mentioned should be too much even for a young shooter if they hold the gun correctly.
Just know that when you use more powder and a heavier bullet, recoil will go up accordingly no matter what caliber you are talking about. If you take everything into consideration, the gun using the most powder and heavier bullet will always have more actual recoil. There are several things that can make a gun feel like it has less recoil just as an example, look at the WSM's. They use about the same load of powder and use the same bullets as the Magnums they are a copy for, but they exhibit less felt recoil.