I think that the mental aspect of the game is often underrated by the equipment-centric posters that frequent this site.
Racquets and strings are very important to those who care about that sort of thing.
Obviously, your nemesis does not. To him, they are just tools.
He's gotten used to using ordinary strings until they break.
He would probably resist modern innovations and, moreover, they'd likely damage his game.
I've seen this in other fields, too.
For example: Pete Townsend uses old school, heavy gauge strings that most modern guitarists would find unplayable.
That what his style was built upon and he sticks with it.
Neos 1000, Eagnas Combo 810