You are right. The lighting tower did have a bug in it. It is fixed now. The lighting tower adds to the damage of all towers in its range. Only one lighting tower will effect a tower, effects aren't cumulative.
I tried Delta in Training mode and still couldnt get past the part where the bat things fly from the upper left corner. I am able to beat the Forest map, so its not that I'm an idiot. Either most maps are too hard or there is some secret trick.