I have thought about this, although I haven't done much experimentation on it. My guess is that insulin works better the more depleted you are. In that sense, it has more of a "job" to do.
Insulin shuttles nutrients towards muscles (or fat). We know that longer and more voluminous workouts increases your muscles' sensitivity to insulin more than brief workouts. We also know that longer workouts deplete your muscle glycogen more than brief workouts.
You mentioned Dorian as an example. For what it's worth, Dorian said he experimented with insulin and didn't find it very effective, he simply got fatter from it, and discontinued it. He doesn't recommend it to current clientele.
Dorian was known for using extremely heavy weights in the 6-8 rep range, with low volume. He very strongly believed in overloading the muscle, and then leaving the gym to recover.
Milos, on the other hand, completely morphed from insulin protocols. He was known for using high volume, and much lighter weights.
Just using really simple high-level "bro logic"... it seems that a depleted muscle from a high-volume workout would respond better to insulin.
If we take the logic to the other extreme: if you give a sedentary obese person insulin in the absence of a workout, it causes almost no muscle growth, they just get fatter.