Nope.
That applies to the person who put up the original video: if he can't support the argument made by the video, he should not have put the video up. The person critiquing the video only needs to support his written argument in a written fashion.
A puts up video.
B says it's bad.
A asks why.
B makes his case by describing why he thinks the video is bad. He makes a claim (e.g. "the red shirt opens himself up to attack, and this is bad"), and cites evidence from the video (e.g. "he opens his left side at 1:35"), possibly citing authoritative sources (e.g. historical texts) if required for authoritative (ethos) appeal (e.g. in 1932, Chen XX wrote "you shouldn't open your left side to attack").
A could legitimately respond with something like, "agreed, but it was a demo, meant to show the form of a specific punch. Normally, red would turn to the right and block," explaining why the move was shown that way.
However, if A were to say, "if you're so smart, why don't you make your own video?" it would be an attempt to deflect criticism from the original video, and would be irrelevant to the point at hand.
Say, if I critique an author's writing, it's not incumbent on me to rewrite the author's work.
Instead, I have to make a clear claim (e.g. "disconnected paragraph structure") then give evidence (e.g. "paragraph 2 ends with a rhetorical question, but the start of paragraph 3 does nothing to suggest an answer, or a direction to an answer to that question").
If, in response, the author wanted to address my criticism, he would have to challenge my claim, challenge my evidence, or challenge the rule on which my claim was based (e.g. "yes, they are disconnected, but the piece was written in a style evocative of X writer, who is well known for writing disconnected paragraphs. It was a parody of that author's work, in other words.")
In a web forum, it is only incumbent on B to make an effective written argument as to why A's video is bad.
Excellent post, needs to be read by all here.