Is McKinsey helping pharma companies to price gouge? Or is it simply advising them to take advantage of the current set of legislation in the most optimal way possible?

McKinsey is not responsible for drafting the legislation. It's simply advising what's best for its clients in the current context. I see it no different than a lawyer advising his clients to never talk to the police - simply because it is allowed by legislation. Or a tax advisor advising his clients on the best ways to minimize their taxes, which is once again enabled by the legislation.