In other words, BYU does own the Utah market.
Bowl games are a joke for comparing ratings because of what you already stated. The differences have been so minimal that there isn't a whole lot you can gain from it.
The numbers that would make a difference in comparison would be regular season national tv matchups when both teams were having relatively the same success and both teams were playing teams that were comparable to each other in following.
It's hard to come by those numbers, so it's hard to prove anything conclusive, but we know there are many LDS members across the United States and while they are not all BYU fans, many of them follow BYU as a second team. Meaning they still watch BYU play. That's where I think the real difference between the sizes of the fanbases comes in.
Also when you look at the state of Utah, look at the size of the stadiums they play in and how many times those stadiums get filled. Utah has made some headway there no doubt, but IT IS, whether Utah fans want to admit it or not, indicative of the following the teams have here in the state. When Utah gets a 60,000 plus seat stadium and they're selling it out on a regular basis I'll believe the Utah owns the Utah market as much as BYU does argument. Until then, it just isn't true.