Just a couple of quick thoughts. Evidence isn't the same thing as proof. Evidence doesn't have to be concrete.
There is nothing at all wrong with accepting that the opinions of some are given more weight because they have established that they are credible. For example, there is not a doubt in my mind that K-man is a credible source for Aikido, Krav Maga and Okinawan Karate.
So, if K-man says, "we do this," or, "i've seen this and it is true," that's enough for me. Is it "proof?" No. But it's reliable evidence.
The hazard here is just to remember that expertise in one area should not necessarily imply expertise in other superficially related areas.
As for chi balls and such, it's like the problem of sunrise. You can't deduce that the Sun will rise tomorrow, because it has always done so. Without using inductive reasoning, we would be stuck. End of conversation... but we can be pretty darned sure that the Sun will rise.
Point is, we aren't in Logic class, and we aren't (or shouldn't) be holding each other to strict logical standards. Inductive reasoning is how we know a lot of things, and even Spock would was guilty of it.

We can have a conversation with each other only if we presume we're speaking to people who know what they're talking about, and give each other the benefit of the doubt, absent evidence to the contrary. And evidence is not the same thing as proof.