@alberto:
i dont have to run any simulation at all. simple math will do the trick.
plus another war strategy issue you missed to point out:
while 100 average people can somehow look after themselfs goup b will be in permanent struggle because 10% need to take care of the other 90%. so you task is not only to kill the enemy but also to defend the other majority.

while matt has pointed out a few good things about how important this "bounds" are for evolution there is just one thing to add:

its the old nutshell about why the t-rex died out and the chicken survived. surviving of the fittests has nothing to do with strenght or self sacrifice.
Most animals dont win by fighting but by hiding or running away. from this point of view the cowards from you example have the best chance to survive if the circumstances are right.

the human body is a very weak structure compared to most animals. we need to rest and sleep a lot, we die very fast without food or water, and so on....

the best evolutional way to make us stronger or "fitter" is to found hordes and a social kind of web.
this grants us dramatic benefits and raises our average age when we die from 30 to 75+.

in nature the principe of lonesome hunters is very weak and not many survive on the long run. on the other hand colonialisation seams to be a key feature that works.

and the reason we are still here is that we are a social species and not the other way round.