Oh, you are right, I've forgotten. There's also a flat mult reduction to all attack values, simply to extend the duration of the battles. Because otherwise with attack equal to defense for most units, battles would end in 1 tick.
The 1 unit strategy is the strat. congratulations for figuring it out. It looks silly, but it's an unavoidable outcome of random targeting. And since I didn't want to change random targetting, I decided to roll with it, so all future battles are balanced around this exploit.