Why did yoy ask this question?
Because that's my argument. So either agree, or find a fault in my reasoning.
The debate here is a complex issue. Non-experts on tennis do not have knowledge to comprehend which argument is more sound in debate about a complex tennis issue.
That's assertion, not argument. I could take a debate about anything and make that claim. X topic is complex issue, only experts on X have the knowledge to comprehend which argument is more sound. Y is an expert on X, because he is widely recognized to have practical knowledge of the subject (take any media personality here). We're not publicly recognized experts, hence just have to agree with Y.
The massive hole in your argument is that you don't need to be a publicly recognized expert to have expertise on a subject. Otherwise only 'experts' could debate anything. And essentially anyone can read and post on MTF, even Sampras himself. When someone presents an argument, they're not saying "believe me because I'm some anonymous internet person"; they're not asking for your faith
. They're presenting a series of claims backed up by certain evidence, for others to evaluate.
Your response is to say "How dare you make an argument on this topic! We're all too stupid to discuss this issue, so lets just blindly believe what this other person says, because he's good at playing tennis".