Whenever I see articles like this, I watch videos like this...
https://www.youtube.com/watch?v=ZbmaEtZeno8
...and I just don't see the difference between that and today's players. I mean, the grips and technique differences are obvious; but the power and level of spin looks exactly the same to me as if Federer and Djoker were battling it out.
I'll concede that there is a difference and that I've felt it myself with poly, but I don't think it's anywhere near as extreme as it's made out to be. 11% is still something, and it can make a big difference at the top levels of the game, but it's not "twice as much". I bet if Nadal strung up a full bed of gut pretty tight he would hit close to the same amount of spin. Actually, if my math is correct, I'd say he would get around 89% of his normal amount of spin.
I also have a personal pet peeve regarding old timers like McEnroe claiming that "It's those new poly strings all the kids are using now!" every time a player like Nadal hits a good shot. Yeah Mac, I'm sure his choice of grip, technique, non-wood era racquet, and fitness level/strength had nothing to do with it.