Be cautious of 'studies' unless you know who proposed them, what questions they wanted answers to, and what position they were trying to support.
I'll be the one referred to here was proposed by the F-16 mafia who wanted their machine for ground support -
Yes, perhaps vulnerability does decrease as the cube of speed, but then again, so does the ability to hit targets precisely. And cost and complexity goes up as the cube of something, probably speed.