Scratch that, reverse it Re: Edge of Tomorrow...
I gave you an upvote for pointing out the WTF in Edge of Tomorrow and especially managing to do so without spoilers, but it turns out that the reason for the problem is actually the opposite of what you suspected.
Allegedly, the original script made complete sense (at least, within the rules of the film) but the ending was much darker. Test audiences wanted a more upbeat ending, and given the constraints of time, budget, and availability of actors for re-shoots, that's what you got.
BTW, it's possible to make excuses for the ending -- and I'm sure some people will do so -- but I agree with you, there's no way to make that ending "right" based purely on the internal evidence of the movie itself.