Forgive me if I'm misunderstanding, but I think you're trying to make things too complicated. What we want to know is "if I send x% off:def ratio, what is the probability the attack will succeed?", or vice versa "if I want a 95% success rate, what off:def ratio do I need to succeed?", i.e. our x-axis would be "offence/defence" and our y-axis is "% victory". That is quite simple to work out once you've made your assumptions about the distribution. For a uniform distribution anyway, I haven't yet tried any others simply because I'm unsure how to test which is accurate.
As for using a CDF, I'm not sure what you're trying to use as your random variable. Maybe I'm being dense, but I don't see how CDF/PDF helps us here.