All of you are correct that muskets are ahistoric. But many other things in the game are unrealistic. People can run without getting tired, and cavalry have perfect control over their mounts. Swords and other weapons never get stuck inside bodies. People fight at 100% with 1 hp and with their blood all over their face and chest. Lances don't break.
Muskets exist in an unrealistic world, and there are many parts of the game that are even more unrealistic than muskets. Therefore, muskets should not be changed to be more realistic just for the sake of realism. If you change muskets to be realistic, you would be ignoring everything else that is also unrealistic and then you would be disrupting balance. If you want WFAS to be as realistic as possible, you might as well play the game called Outside.
Changing things for balance and fun are great decisions. But using realism as a reason? As long as they are "good enough" and don't break suspension of disbelief of the average gamer (i.e. shoot homing laser beams) they are realistic enough. And if you get killed by muskets, try running around erratically. It works almost all the time.