Well, it'd not be a decision, but a diagnosis. But I get what you're saying. It'd be a matter of the number of criteria met and the level of problem it causes in one's life, so it wouldn't matter if "most of" the symptoms were bipolar ones. Does that make sense? Doesn't matter which outnumbers the other -- if enough criteria were met -- for one, the other or both, the respective dx(s) would be appropriate.

I DO think it matters, but don't really want to go into the whys atm.
That aside, it's important the treatment works for one's symptoms.