It is about tennis, but I use math as an analogy. Say you have X-Y > A-B. You simply compare two differences where one's value is greater than the other. Let's put numbers... 240 versus 35. Can you tell me something about X or Y or A or B individually? Of course not. We'd need either literally the value of one of each pair or further equations to compute them to find out how each is worth. Well, this is exactly what happens when you compare players from different era using simply results. There's a finite amount of tournaments and players compete against one another: the results tell you about the gap between them, but nothing about them individually. You wouldn't do that in a math exam, why don't you use the knowledge you acquired at school and avoid falling in that same trap when we swap words and call this "tennis statistics"? Saying Federer had weak opponents because he won so much is as dumb as saying X must be worth less than B because 35 is smaller than 240... it's the exact same thought structure, just swap numbers for statistics and letters for players. So, let's give this logical fallacy a name -- the ERA fallacy. It's a type of non sequitur that occurs when jumping from a comparison of differences to the qualification of the individual elements contained within. EDIT Regardless of my opinion on any subject, logic speaks. If the facts are coherent with many explanations, you have no reason to bump one out and doing so is a fallacy. You need other inputs to narrow the choices until only one remains.