Rambam and R' Hai Gaon say that Gemara is authoritative because of minhag, but are there other opinions as to the reason? The one that I'm familiar with (or that I most identify with) is the reason that the Gemara is authoritative because it's simply the best index of the actual halacha (and what Chazal said). Is there anyone that takes this viewpoint? Rosh? Rama? Am I being a halachic idiot/outcast on this?
I don't think that this is a bad question at all. I'm aware of two explanations:
(These are a bit complex; I'll explain in greater detail if you want me to)