It's ridiculous that knights and longswordsmen are more combat effective than musketmen. Historically knights were phased out explicitly because you could field a much larger group of musketmen for the same cost with a fraction of time necessary for their training. Also, except at long range, armor could not stop musket balls and disciplined arquebus and musket wielding troops would destroy a mounted charge (Japan during the Sengoku Period is the best example). Muskets costing 30 production less than longswordsmen in Civ 5 does not capture this at all, because all this means is that they build in 10-11 turns instead of 13-15 turns (oooooh boy).
The way this can be incorporated in the game is to give +33% strength modifier to musketmen, riflemen, and cannons when they are fighting against units from civs who have not researched Gunpowder yet.
The way this can be incorporated in the game is to give +33% strength modifier to musketmen, riflemen, and cannons when they are fighting against units from civs who have not researched Gunpowder yet.