It's not just you: uinfortunately, the game does not encourage diversification enough. Worse still, some tech paths are just far from optimal.
I have stopped updating this game years ago, but I've worked on a sequel that greatly improves on the flaws you noted (i.e. there's a progress bar that gives a rough estimate of when the next enemy wave comes). Waiting for when I'll be able to afford an art designer.
Long is the journey until the concept reaches its full potential, and feedback is vital to adjust the heading, so thanks :)