Kathryn could have gone back and saved every one if she took the time find a more reliable method of time travel or just followed Voyager around from Caretaker under Cloak... Hours, maybe minutes before anyone was destined to die, she would replace them with a robot and then Admiral Janeway could much later revive all the saved crewman from transporter stasis after her ship, and Voyager got to the Alpha Quadrant, which hopefully wouldn't muddle the timeline too badly. Sure it's a new timeline literally, but the corner stones of history up to the point she went back would remain identical.
Look the fuck at what THEBILLMURRAY could do with enough foreknowledge in Groundhog Day. Meanwhile Janeway takes all that power from knowing exactly what's going to happen next and she flushes it down the toilet by steering history into uncharted waters so that she's immediately just as ignorant as everybody else.