Thanks so much for taking the time to review! I 100% agree with you on all of those criticisms. The tutorial could definitely do with more fleshing out, and I already have an improved design in mind for the power UI.
You're definitely right about the tedium of running back and forward. Perhaps just adding the ability to select a tower to place with number keys or something would fix that. That way you could still get cut off from the exit by the gates, but wouldn't have to keep running back to pick up towers.
I'm not sure if or when I'll have the time to update the game, but I will let you know if I do!