All I can say is that it's their product and their job to produce and distribute it.
Sure. The buck ultimately stops with them.
You could say that they're incompetent for not finding a way to manufacture more, but as the Wall Street Journal speculates, the only way might be to try and outbid for components which could mean selling at a loss.
So we have a situation in which you could either say they're incompetent for not outbidding Apple, or they're incompetent at making money on their flagship product.
I'd rather look at things more holistically and say that the situation just is what it is right now.