It is easier to take a raw recruit train him in the manual of arms, and to march in formation, then to train a bow, or swordsmen. A good bow, or swordsman can take years to reach proficiency, a musketeer takes months. The necessary level of fitness, and strength to be a bow, or swordsmen is higher then it take to be a musketeer. It's handier to use a musket with a ringed bayonet then a 14' pike. It's easier to maneuver a formation of musketeers on a battlefield, then a pike formation. A pike formation is more vulnerable to musket or cannon fire then a musket formation. Imagine a battle between the Round Head Army vs. Marlboro's Army, who would win?Wasn't your initial argument that guns only supplanted bows because they made it practical to press large numbers of less-trained soldiers into the field, bows being superior in every other respect? If that were true, then logically the profusion of guns in warfare would have to coincide with an expansion in army sizes, that being the only rationale we accept for their adoption. But that didn't actually happen, and if anything, armies in the age of gunpowder became more professional and dominated by mercenaries, which throws your premise into question, to say the least.