It’s not like Borderlands, where there is a infinite amount of new but also more ore less the same weapons with differing numbers! You can upgrade (called tinkering) any weapon with money. It costs more with each upgrade and only upgrade it five levels above your own, so you can’t just grind money and get overpowered. But yeah, you can finish this game with one gun you like!
Na, no rose colored glasses needed! The first Golden Sun is one of my favorite top down “classic” jrpg. I replayed it a couple of years ago on my old Ds (the one where you can play your Game Boy Advance games) and it aged really great!