<<Whether somebody "can do it better" should not have any effect on the validity of the critique. >>
I agree. For example, Baudelaire was a great poet, but despite only writing one (early) novel his criticisms of novels are forcefully argued and convincing. His taste in music was also good-- he championed the "music of the future" of Liszt and Wagner-- but those opinions are only convincing because of the intensity of his belief. He also wrote about painters. He was an all-around "aesthete", meaning he had a good eye and ear for the beautiful without being an expert in anything but poetry. I doubt his views on painting are still as valid as his views on writing.
<< I use my "crooked-wall example" above: the fact that one critic knows how to build a straight wall, whereas another one does not know how, does not change the evaluation of the wall. >>
Samuel Johnson said something to the effect that "I may criticize the workmanship of a table without being able to make a table. It is not my business to make tables. It is his." So Samuel Johnson obviously agrees with you. And I would never dare to contradict Samuel Johnson. He lived at a time when poetry, and art in general, was governed by a strict set of rules. He probably would not have cared for the Romantic age, when all the rules were set upside-down. When the rules are not clear-cut anymore, the only way to tell who is "right" is the one who can actually create something good: not the simple critic, who can do nothing.
<<This gets into a different direction. The fact is that "critique" nowadays means finding flaws, not praise. It wasn't always like that, though. >>
If you insist on your own individuality and the rightness of your own beliefs, you can become a prig, overbearing and intolerant. Actually Samuel Johnson was something like that, but he was an amusing and intelligent prig so modern readers can forgive him. On the other hand, if you flatter others, or meekly follow along with what others are saying and doing, you are a coward. There's so much to say on this subject, but it's not really piano-related