No dis-respect meant to Messi, but he wouldnt have been any player at all without modern (totally legal) medicine - so he is a "product" of his time.
Neymar, hmmm it is stil his speed and agility /control that makes him the player he is, yes with different (weight) of ball he would possibly be slower and maybe require a little more muscle but he would still be the agile player with the great touch etc he is now
Would he have the same touch in a pair if heavy 70's boots and would he have bounced up like pele did after some truly brutal treatment? It's always fun to compare as we will never know! Pele would have been a different player if he was in his prime today fitter faster and I 'm sure he would have loved the moder balls and boots.
Apples and oranges comparison but fun none the less!
Kloser is a funny one his domestic goal scoring record is a bit meh and his contribution outside the penalty box minimal at best but he excels at scoring goals and seems to love the big occasion in the shirt of his adopted country! Muller gets similar criticism I think it was Ferdinand who said that playing against him if he's outside the box you just let him have it as you know nothing will happen.