think of "as well as" as "also" or "in addition to". So, "as much as" would mean that they are equally good friends. No one is closer to John than the other. And "as well as" would mean that both are Johns friend. How good or bad friends they are is not important.

Thank you for your help!

'as much as' is speaking in terms of quantity, so John is just as good a friend to both people, as opposed to be more of a friend to another. 'As well as' just means John is a friend to both, it doesn't concern how much of a friend. Does this make sense?