I'm not a practicing Buddhist but one of the principles of the Noble Eightfold path is the idea of 'right livelihood'. Which essentially means that you should avoid making a living doing something which does harm to other living things. One of the listed livelihoods to avoid is being in the business of making weapons. This really struck home when I was working for a company doing a lot of DARPA work. I had previously…
I used to work for a university supercomputer center, which (surprise, surprise) ran weapon simulations. I agree with you, though some DARPA research to "kill people better" does good by reducing collateral damage.
So I agree with you that "killing people better" does "save lives" in a sense (although no war would be the preferable option of course).