See, what I have a problem with is that in order for a pony to fire that musket he has to stand up on his hind legs, lift the gun to his eye with hooves, and pull a trigger SOMEWHERE without any fingers (and I'm not gonna bother mentioning that any musketeer worth his bullets closes their eyes when firing). And if he wants to hit what he's aiming at, he needs to balance on his hind legs long enough to line of the sights, as well as brace himself for the recoil. Balancing on hind legs is hard enough on a quadraped, doing so while firing a gun is nothing short of miraculous.
I know the Equestria Prevails isn't trying to reinvent the musket just for ponies, he's just drawing cool pictures; and it is cool. I do like the idea of ponies fighting eachother and griffons with shot and powder weapons, but to picture ponies fighting with weapons like spears, swords, and guns (i.e. designed for humans and their opposable thumbs) with hooves (or Celestia forbid, their mouth) stretches my willing suspension of disbelief.