Soooo.... just thought of this huge plot hole

It is worse than you say,. Thor could bring his planet back,. Wanda his brother

The writers and directors both have stated repeatedly that certain damage done by the stones is permanent, and can't even be fixed by the stones themselves.

The stones couldn't reverse the damage done to Banner's arm and couldn't reverse Tony's fatal injuries, because the stones' energy itself caused that damage.

That said, you do raise an excellent point. What is "undoing the snap" if not reversing the damage done by the stones?

And, as you point out, the only "everlasting sacrifice" is that required to OBTAIN the soul stone, not WIELD it. Red Skull says this explicitly: the sacrifice is necessary to teach the wielder to respect the soul stone's power. Once taught, it hardly makes sense for the wielder to keep learning the same lesson over and over with each use.

This is why no one should ever touch time travel again in movies. It always results in plot holes. I didn't realize this plot hole before but you are right and I can't stand plot holes. Now I will lose even more sleep tonight