18650’s loose slightly more power than alkalines if they’re sitting on a shelf. However, 18650’s and CR123’s will have about twice as much power and runtime compared to alkalines so they’re great for high current applications such as flashlights, so yes, they will last longer than 3xAAA battery configurations.
Check out this thread for more info about li-ions:
You do need to be careful about rechargeable li-ions because they can get very angry if not handled properly.