Shannon built on Hartley, as much as Einstein built on Lorentz.
That's not to say these weren't great minds, but the concepts where in the air and the race to formalize them was on; most of the "second places" are today forgotten or their contribution diminished from the modern "winner takes all" mentality, but none of them existed in a vacuum.
The history of science is fraught with independent discoveries, from calculus to the the telephone, up and including mass energy relation and the basis that later became quantum mechanics.
If A and B made the same discovery independently, that is evidence that A was replaceable, but that C built on D is not evidence that C was replaceable.
That's not to say these weren't great minds, but the concepts where in the air and the race to formalize them was on; most of the "second places" are today forgotten or their contribution diminished from the modern "winner takes all" mentality, but none of them existed in a vacuum.
The history of science is fraught with independent discoveries, from calculus to the the telephone, up and including mass energy relation and the basis that later became quantum mechanics.