Any answer to this is going to be pure speculation, and continue to open up "what-if" scenarios, but here goes:
An important outcome of this Endgame is that the stones are GONE, and the avengers only suffered two losses (3, counting <PERSON>). In any timeline where they use they defeat <PERSON> before he snaps half of reality, the stones still exist. In any timeline where the stones exist, they are a threat. A number of beings more powerful than <PERSON>, or the avengers, will want to get there hands on them to wipe out all of the universe or remake it in there image. Any future where they kill <PERSON> and then the universe is completely destroyed by another force is probably considered a loss to <PERSON>.
But wait, you say, once they kill <PERSON>, they can just use the gauntlet to get rid of the stones themselves! Not so, say I. 516
The only being besides <PERSON> who is shown to use the stones without suffering death is the <PERSON>, who is in no mental state to do the snapping. But wait, can't one of the avengers just make the self-sacrifice play to get rid of the stones? No, the only being who can physically fit into the <PERSON> gauntlet is <PERSON>, so another avenger can't just throw on the glove and take one for the team.
What about <PERSON>'s nanobots, can't he make a nanobot glove? Sure, he can reform the bots into a glove shape, but without time to analyze the gauntlet or gather info from <PERSON> about how the glove taps the power of the stones and how to wield them, his prototype is just as likely to blow up as it is to work.
and thus the argument continues to spiral further and further downward, when the core of the issue is that <PERSON> plan was the only way, because we are told it's the only way. We can spend hours and hours theorizing about how each of the "obvious" plans would have failed and put the universe in a worse situation, but it's unnecessary. The other plans would have failed, because both Doctor <PERSON> and the <PERSON> brothers say they would have failed. The actual reasoning behind what would have caused each of them to fail is moot. 516