They used to use majority save, and it didn't work. Then they used wound allocation where different models had to make saves before you could double back up on one, and it didn't work. Now they're working from closest to closest, and so far it's working.
Yes, you would check to see how many models are within 6" of the character doing lookout sirs and you would only roll that many each time, but it does not significantly increase the amount of time you spend resolving the wounds in my narrative.
I don't see how additional characters matters, once you looked out sir'd the wound you don't get to pass it off again. If the other character has the same save as the rest of the unit you roll it together and there's not difference. If they have a better or worse save, I guess you roll that model's saves one at a time until it fails or you pass them all. Either way, that particular situation doesn't happen all that often.