A big part of the success of our gun laws was the buy back and periodic amnesties. Even if the US of A did this they would barely get anyone handing over the AR15s and equivalents because those who own those believe they have the right to have them. If they outlaw the weapons then again many will hold them, they will just hide them away. That would stop the likes of Uvalde with a new owner buying an AR15 but not stop them from buying a rifle with magazine so potentially fewer rounds and slower killing speeds.
I honestly don't see how this can be fixed all they can do is reduce to some degree future harm.