Thanks for your feedback!
Definitely agree with you, the "currency" mechanic is highly unbalanced and need some adjustments haha
Due to time constraint it wasn't possible to make it as good as i wanted, so I chose to let it be very forgiving to players, so it was possible to everyone finish every level with relative ease
The targeting logic was every tower would focus the unit that was in the front of the line, except for the cannon, that would shoot in the position the first unit was in the moment it started to shoot, maybe this part need some tweaking!