Maybe I was not polite, but you have not shown that any of my arguments were wrong.
Maybe it's strange, but as I said above, you have not demonstrated that any of my arguments were incorrect.
I wasn't trying to show your 'argument' was incorrect; I was merely commenting on the way in which you have conducted yourself in this thread.
Your 'argument' is that you yourself do not have the knowledge to make a judgement on this issue, so have to rely on experts. And really no one can disagree with that, because no one has any special insight into your knowledge or mental state.
This was your original argument: "Pete Sampras has high level practical understanding of tennis. Tennis expert is a person who is very knowledgeable about tennis. Therefore, Sampras is an tennis expert".
Now we have established that being a "tennis expert" does not make you "tennis predictor" and thus does not qualify you to "make accurate predictions about future tennis events". This means that in order to rely on Sampras to "make accurate predictions about future tennis events", proving that he has a high level practical understanding of tennis, is not sufficient.
You must also prove that he has "a good understanding of past statistical trends, and the ability to take into account unknown variables". You have not done this.