In the future you'll only be able to take one weapon with you (for now you can use both weapons just so I can test them in the game easily). There will be weapon arts as well that are unique to each weapon so the sword will probably have stronger stuff. We also debated having it reflect projectiles a la nuclear throne as well. I actually prefer the sword when I test because it does more damage and one shots the basic guys, so once you know the patterns it's kind of a cakewalk. Good to keep in mind though!
The boss lag I'm aware of, I think his shield is using precise collision checking per frame or something instead of a rectangle which is why it gets so rough there. It's on my list of things to fix.
Next will be props in the level that can be broken/add some flavor to the background as well as spawn some enemies potentially. After that will probably be character abilities/upgrades ("aspects" and "pacts"), since the weapon arts will require unique animations.
Thanks for the feedback, it's really appreciated!