BTW, nothing wrong with stem shifters. I've used them. But if you try bar end shifters with swept handlebars I'm betting you'll like them.
Main advantage is keeping the hands on the grips while shifting, if anything unexpected occurs - rut or pothole, debris, etc.
I'm not sure I'd like bar end shifters on drop bars (I'm about to find out with a road bike project) but they're darned near perfect for swept bars.