Well, certainly no more (and I'd say less) "flawed" than trying to draw conclusions about the success of iOS 7, let alone how good it is, from numbers of new device that have been sold.
And, certainly all of what you said undermines your comments even more in relation to stability of iOS 7 vs. iOS 6 based on your personal experiences.
So, I guess all that can be said then is that we can't really argue if iOS 7 is more or less stable (or even overall better or worse) than iOS 6 in a general sense--it's the personal experiences that really matter to people who are affected by them (as it really doesn't make something better or worse for those people if someone else is not having the issues they are having or is having some issues that they aren't having).