Yeah I think it definitely has the problem of being a little unintuitive considering some mechanics work pretty differently from other TD games. I think the cannon does scale better than the other 2. And I'm currently thinking I want to emphasize the blobapult as more of a support/mobility tower. I'm thinking maybe make the slow upgrade more immediately accessible and reduce it's damage a bit so its role is more clear.
Thanks for checking it out! I appreciate the feedback.