It’s interesting you mention your 40 time too, because generally speaking weights SHOULD benefit the drive phase/acceleration phase more than any other part of a sprint, and a 40 yard is essentially just that.
I agree with the skinny fast guy thing, I see that on almost a daily basis
Weights when periodized properly and planned properly at proper volumes should be helpful generally, but how helpful would all depend on the person. I know one guy who went from 11.7 to 10.8 in a year and he swore that it was cause of his extremely improved deep squat.
and at the same time, a guy goes from 11.2 to 10.6 and isn’t touching a barbell or a dumbbell at all.