For the record, I do believe Brian used Rotosound strings in the 70's. I recall an ad that appeared in one of the guitar magazines in 78 or 79 that depicted various guitarists and bassists, and one of them was clearly Brian.
Later, in the 80's, I remember seeing an ad in Guitar Player (ca. 84 or 85) for Superwound (which were actually made by the same company as Rotosound, I believe) with several guitarists including Brian.
This does bring up an interesting point, as I've always felt the best way to get a really good guitar tone is to heavier strings, nothing lighter than a .10 for a high E (I personally use a .11, and have lately thought of go up to .12's).
Brian, of course, uses as .008, which I think is about as light as you can go with guitar strings (I recall seeing an article where one of the guys from Judas Priest is quoted as using a .007, but I don't know if that's actually true or if it was just a misprint or what).
At the same time, the Red Special, as I recall has a 24 inch scale length. Compare this to a Les Paul with a 24 and 3/4 inch scale, or a Strat with a 25 and a half inch scale. Generally, guitars with such a short scale are considered to be built for children and adults who can't quite reach as far up the neck on most guitars (interesting thought: how tall is Brian? Does hea he have shorter than normal arms?). The trade off is that you don't get quite the kind of rich tone that's generated by an instrument with a longer scale length.
Yet, Brian has some of the coolest guitar tones of all time (he was even cited in an recent overview of the greatest guitar tones in Guitar Player).
So, you can talk about the generalities of gear and how this particular guitar or amp or gauge of strings affects your tone in this or that way, but you hand any instrument to a guy with a magic set of hands and BOOM!!!!
BTW, there's lots of people who play Strats who sound NOTHING like what you hear old Elvis records. Off the top of my head, there's Ritchie Blackmore, Jeff Beck, David Gilmour, Terje Rypdal, Steve Hillage, Rory Gallagher (RIP), Gary Moore, Stevie Ray Vaughan, etc.
"Compromise? That word is not in our vocabulary"-Roger Taylor, quoting Freddie Mercury