Oh, I quite agree about the rarity of rifles in the prior to about the 19th C. And what curators of the past did is, to my mind, awful. But there as also many surviving examples of military arms "in the white," in public and private collections which have not been touched. I'm not disagreeing, simply stating that both were used.

As for accuracy in muskets: when you load a .65 caliber ball in the .69 caliber musket by dropping the ball into the barrel and seating it by whapping the butt of the piece on the ground, loading is indeed speeded up but accuracy suffers a lot. Most muskets (i.e., smoothbore military flintlocks) simply weren't accurate beyond 100 yards -- being shot by one beyond that range counted as an accident. Granted, if you have enough balls flying around folks are gonna get hurt or killed where ever they are, and that was the rationale for the massed unit fire.

A brace of pistols, a sword, a pistol and a longarm, a longarm and a bayonet -- when you've got one shot you need backup weapons in combat.

It occurs to me that riding around on a horse while carrying either a rifle OR musket would be cumbersome at best. A musketoon, a blunderbuss, a brace of pistols, fine. But I'm having a hard time figuring out how you'd carry and use a flintlock weapon at least 48 inches long from horseback...especially in a fight. (Yes, I'm aware that it's possible, only that it's akward with a loooooooong gun.)