of course the pros also tweak their racket (MINOR changes) depends on their needs or age limitations. rec players should do the same.Do you really think people who's livelihood, career and legacy depends on their tools haven't tested everything?
If Djokovic would play better with a light racquet, he would be playing with a light racquet.
Do you think 5.0s became 5.0s by accident? Or maybe they put in thousands of hours of work and experimented with technique, strategy and equipment.
Why would they trust the opinion of one racquet shop guy and not their own body and experience?
what's that has to do with playing with a heavier racket than the one that will benefit your game the most?
a 5.0 player should also stick to the racket that fits his level (and it's probably heavier than what a 4.0 needs)