Yeah, some balance is definitely needed. It's way too difficult. I've made some balance changes already, like lowering the spawn rate of penguins, making ice melt slower, and increasing ice harvest speed and I think it plays better now. I don't think I can update the project during the voting period though so those changes will have to be uploaded after the jam is done.
I agree with being able to upgrade your cannon's stats in the shop. It's something I wanted to do but simply didn't have the time. Thanks for playing and sharing your feedback!