Or, is one of my original premises wrong?
Nope, you're pretty much on the money for the bit on the bayonets. What does help there is that soldiers with muskets at least have an alternative to the bayonet (indeed, we have multiple instances of military authors bemoaning soldiers' tendency to stand off and shoot it out instead of getting in there); without that alternative, the dimensions and mechanics of combat are a bit different.
I commend to your attention the following previous posts on said dimensions and mechanics:
As always, if anyone else would like to write an answer of their own, please don't let this post stop you!