Who says the same daughter would not have been born in the timeline where thanos had been stopped?
Tony. The Ancient One. Banner. Leopold Fitz. Gemma Simmons.
Did anyone offer proof of that
Yes, multiple characters in the Endgame movie, that's why returning the Infinity Stones to their correct time is so important, it's explicitly spelled out in the conversation between The Ancient One and Banner. Changing/removing one of the stones would change how reality moved forward. Only by returning it to roughly when it was taken would this be prevented. Technically something removed only needs returned before it affects something else, so the Tesseract being removed from Area 51 only needed returned before someone did the next test on it for something. If months passed between tests then in theory anyone taking the Tesseract out of the timeline could return it from any point it was taken to before the test because it wouldn't change anything that happened, barring cosmic events which just add on other stipulations because of how all the stones are tied to reality. Something more mundane would have far more leeway just how long it could be missing.
What they could have done is simply taken Morgan, and anyone else, into such a timeline where Thanos was stopped since that's how the Quantum Realm worked. Yes it allowed time-travel, but it also allowed time-bridging. That was the entire point of Tony making the time-travel GPS, so they could accurately return to their original starting point. It could have easily been used to plot out a course from the Snapped 616 universe to one in a different time and space, be that 5 years prior or whatever. But that would have meant a far shorter film that basically turned into a house moving.
Tony. The Ancient One. Banner. Leopold Fitz. Gemma Simmons.
Yes, multiple characters in the Endgame movie, that's why returning the Infinity Stones to their correct time is so important, it's explicitly spelled out in the conversation between The Ancient One and Banner. Changing/removing one of the stones would change how reality moved forward. Only by returning it to roughly when it was taken would this be prevented. Technically something removed only needs returned before it affects something else, so the Tesseract being removed from Area 51 only needed returned before someone did the next test on it for something. If months passed between tests then in theory anyone taking the Tesseract out of the timeline could return it from any point it was taken to before the test because it wouldn't change anything that happened, barring cosmic events which just add on other stipulations because of how all the stones are tied to reality. Something more mundane would have far more leeway just how long it could be missing.
What they could have done is simply taken Morgan, and anyone else, into such a timeline where Thanos was stopped since that's how the Quantum Realm worked. Yes it allowed time-travel, but it also allowed time-bridging. That was the entire point of Tony making the time-travel GPS, so they could accurately return to their original starting point. It could have easily been used to plot out a course from the Snapped 616 universe to one in a different time and space, be that 5 years prior or whatever. But that would have meant a far shorter film that basically turned into a house moving.