it doesnt do anything if you go down to 50% though

your initial point is that the first mover gains an advantage because the second mover does less damage in return

but for the second person to do less damage they have to be knocked down "enough" which is to 16% of the first persons buildings

or about 27% under the absolute most favourable conditions so somewhere between 27% and 16% it begins to kick in

at 50% it does nothing new