Sampras in his retirement can be seen playing fine with polyester strings, and he still comes to the net on these plexi-cushion aka flexi pave courts (slowed down rubber courts). That man's serve can't be tamed because his serve is just so dam heavy. He's even beaten federer a couple of times on these style of courts in exhibition matches to date.
They slowed the courts down because of money and to remove American dominance. Advertisment clients wanted more exposure. If a big hitter or server like Roddick or Blake was destroying opponents in a piddly 1:20 mins. The advertisement slots weren't exactly plentiful. And they demanded the games to go longer.
They even created phony backlashes from the "public" saying that racquet technology has become too powerful and is ruining the game.
Which is actually not true because pro players racquets are quite lower powered and its the average joe racquet (which pro's wouldn't even touch and hardly ever gets restrung for control) which are the over-powered ones launching balls into the back fence with no chance of returning serve.
Agassi was such a good returner generally - and it was further enhanced by using a hybrid of spin friendly kevlar and gut strings.
And Rafter with full gut setups was a tremendous spinner of the ball.
- I argue that polyester strings haven't changed the game as much as putting metal in the balls, and slowing down the courts... doing those two things created a gap in the market which is why polyester strings were able to break in.
Yes, we know it's all about the technique. But if your racquet collapses every time you volley..you need to add some lead to it...