As you've noticed, the mortar is only good at shooting still targets. To make up for this disadvantage, it's also capable of killing multiple enemies with one hit (area damage, up to 5). I programmed it this way with an aim to have other weapons that worked differently in the future, but we ran out of time near the end so we stuck to one mortar and troop deployment.
You make a good point, the mortars are annoying when they miss!! Thanks a lot for the feedback, I've just pushed an update where they never miss their target, and to keep things balanced I boosted the enemies too.
Your feedback is appreciated! Also, thanks for playing till the end! We're glad to hear you enjoyed the game :D