Instead of notching up the difficulty level you should increase the probability and amount of seam adjustment even for skilled bowlers , currently with skilled bowlers (70+) we can bowl peaches and jaffas 5 out of 6 bowls in an over with the new ball hence too many edges and wkts which is not incorrect either because if you can bowl such amount of peaches you deserve those edges and wkts , if there is more adjustment to seam then there will be less peaches and jaffas hence less edges/wkts , more over it will be more rewarding/satisfying if you bowl a peach that result in a wkt.
Moreover if you just increase the difficulty level then edges will feel like random and there will be "He just played my previous peach of an outswinger just fine and now with similar delivery he nicks it"