obviously archers would only give about 1% of the points than mars units would give
defeating 1 archer gives 180 battle points (+20% if enthusiastic)
a mars unit 15k (champion 20k)
ranking points are 1/50 of battle points
so donating one archer should be equal to defeating one archer
that would be 4 ranking points
that is a little bit more than donating 1 iron age good
I don't see how placing archers can be exploited
you donate 100 times archers
another player one time mars champions. more points
so placing mars units could be exploited
will be like the big exploit of donating ropes or paper because they have the smallest goods building