I find it inspiring that you continue to be a tennis fan while being blind... It's really quite hard to appreciate the sport without being able to see things
In all seriousness, to reply to your argument: you really didn't need to make it so convoluted. You could've just said "mid 30s Fed and Djok were top 5 players in the world. How much worse could they have gotten?" And everyone would have to agree that best on the cold, hard facts, they only must've lost a small edge.
HOWEVER... and it saddens me to repeat this claim which has only been mentioned here ad nauseam... At this level of tennis (and many other endeavors) LITTLE EDGES MAKE A HUGE DIFFERENCE. Allow me to repeat and rephrase: FINE MARGINS DETERMINE ALMOST ALL TOP LEVEL MATCHES.
Did you get it? Need I repeat it again? Let me give an example. Remember the 2019 RG SF between Nadal and Federer? It was a routine straight set affair for Nadal: 6-3 6-4 6-2. What percentage of the points do you think Nadal won? That's right: 56%
https://www.atptour.com/en/scores/match-stats/archive/2019/520/ms003. So Nadal basically won 11 out of every 20 points, Federer 9.
Care to wager what the margin was for the 2007 FO final? That's right, 53% to 47%. Nadal won less than one more point out of every 15. I just chose these two matches, but you could repeat these with many matches. Actually even in the most absurd beatdowns (say, RG 2008 F), you're unlikely to win 2/3 points.
Anyone who has statistically analyzed tennis will tell you (and this has been posted many times) how much more dominant is a player who wins 56% of points over a year, compared to say, 54% of points.
So bottom line: yes, no one is saying Federer and Djokovic are suddenly losing challenger-level matches in their mid 30s. But if they're losing 2% more of their points, that is a meaningfully huge difference.
Thank you for attending my TED Talk.