To me that actually sounds more condescending. The statement form suggests not only that I thought of the right way to solve your long-term problem in 5 minutes

To me that actually sounds more condescending. The statement form suggests not only that I thought of the right way to solve your long-term problem in 5 minutes, but also that I'm confident you didn't know about it. The question form depends a lot on tone, but at least it admits that you might have considered the idea.