Nah, I don't think Yuna would be too similar to Laguna if she had her gun. Yuna has pistols, and Laguna obviously prefers the Big Guns. An FFX-2 style Yuna would most likely be able to switch between dresspheres much like how Cecil can switch classes. Besides, look at all of the characters with blades for weapons

Summoner Yuna would be pretty cool though.