Here's a hypothetical that proves your statement "speed of the court is irrelevant" makes absolutely no sense.
Let's say Federer and Nadal are going to play a best of 3 set match and if Federer wins this match you, Gary20, will win $1,000,000 US dollars. And, you Gary20 get to pick the surface from Wimbledon 1st week grass, Cincy Hard Court, WTF Indoor, US Open hard court, AO hard court or RG red clay. What would you pick? Any one that knows these players would pick Wimbledon 1st week grass or Cincy Hard Court because these surfaces are best for Federer and not as good for Nadal. If you got $1,000,000 if Nadal won and you could pick the court, you would pick RG red clay. All I can say is I certainly would pick the courts as I indicated if I could win a $1,000,000.