I know that he did wrk at G&H, but that doesn't mean his suits had amazing construction.
That is, once he started his label, it doesn't follow that he had his suits made to G&H standards.
Keep in mind that most fashion labels (Prada, D&G, Gucci) have so-so construction in their suits, with a few exceptions.
Construction isn't paramount for many labels.
I know that most fashion houses do not have high quality construction, but I believe that McQueen is slightly above the others. Obviously you pay for the design as well, but there's definitely carry over from G&H.