The last half of his statement is especially invalid in roughly half of the world. Bill Gates isn't very strong, and he's more useful than any 'strongman' I've ever heard of.
See: Einstein, Newton, Aristotle, Tesla, Edison, Stephen Hawking et al. Brain has proven to be vastly more important and useful, than brawn, for thousands of years.
Bill Gates being particularly strong would not add anything to his overall value proposition, in fact I'd argue it's entirely irrelevant.
Bill gates is strong, he's not Arnold but he is strong enough to maintain his health which allows him to focus on solving actual problems. Everyone you listed except for hawking was relatively healthy(strong) and his specific situation is basically a miracle of modern medicine.
A stronger Bill Gates would be more resistant to disease, death, injury etc., and thus be more useful (which is what this study is saying). If he hurts his back because he wasn't trained and is thus unable to travel and work as much, or recovers from disease more slowly because he is weak then it's really not irrelevant. Bill Gates spends an hour ever morning on the treadmill. If he swapped that for strength training or even half of it for strength training it is likely he would get a significant mortality risk reduction, and thus keep his brain in a position to be more useful for longer. Mind body link, no point in choosing one side or the other. It's all one thing.
Presumably even Bill Gates needs to lift the odd pile of books or open a jam jar.
And I wouldn't swap with Stephen Hawking, so presumably I value my strength levels and lower intelligence more highly than his much, much greater intelligence and virtually non-existent strength.
“Strong people are harder to kill than weak people and more useful in general.”