Lang Lang is an amazing pianist. Don't let anyone tell you otherwise, unless they are an even better pianist than he is.
We're talking about professionals, though. It goes without saying that the guy has talent, but I don't see why you have to be better than him in order to criticize. I don't know your reference points, but saying Brandon Weeden is a poor NFL quarterback is the truth, whether the person saying it can even throw a football is irrelevant.
Also, I doubt anyone is attacking his technical ability. I personally find many of his interpretations to be ghastly.
Bad taste is bad taste, no matter how fleet your fingers.