You're right that the cannonballs could be more predictable, I'm just not sure what system they should follow instead. It's probably not something very hard to code, just hard to imagine how exactly it should work. Feel free to suggest how you think they should work. "Pacing issues near the end" is so vague that I feel unable to act on it, it will not be my main focus for now, but devising a better system for the cannonballs is doable.
Thank you for playing :3