Honestly, I think that fewer hammers to build (Karolin) is a much bigger advantage that 1 extra movement (Muskateer). There are other UUs in Gold that are cheaper to build but they are also weaker. Karolin has the best of both worlds. You can much more quickly build a group of 5-6 gunpowder units to overwhelm the enemy. The French may get there before the Swedes, but the Swedes will be arriving in larger numbers.