Ingenuity -used- to make the recipe's level drop to equal yours, and Ingenuity II made the level equal (your level -3). This made i70 recipes -phenomenally- simpler. The "adjustment" was a nerf plain and simple, to make Ingenuity and Ingenuity II give a flat decrease to the recipe's level instead of taking the new i90 recipes and making them temporarily no harder to make than a simple militia cuirass.