I find this notion that one is "cheating themselves" if they don't throw a mixed bag a false narrative if for no other reason than it puts too much emphasis on the 'arrow' and not the 'archer'.
One could argue that consciously throwing only one company's discs does the same thing, perhaps more so. Saying it has to be Company X and no other seems to put more emphasis on the "arrow" than saying it doesn't matter what company makes the disc as long as it flies.
I don't think anyone is making the argument that everyone should absolutely throw a mixed bag. If you get to a point where you have a one-company bag organically and it works, so be it. More power to you. No sense in aiming for that end right from the start, though.