In order for the plan to become not-brittle, some part of it other than the use-Godzilla-to-fight-Mega-Godzilla part has to “do the hard part” of alignment
You could probably bolt a Godzilla-vs-Mega-Gozilla mechanism onto a plan which already solved the hard parts of alignment via some other strategy, and end up with a viable plan.
What I would actually claim is roughly:
Godzilla plans are brittle by default
In order for the plan to become not-brittle, some part of it other than the use-Godzilla-to-fight-Mega-Godzilla part has to “do the hard part” of alignment
You could probably bolt a Godzilla-vs-Mega-Gozilla mechanism onto a plan which already solved the hard parts of alignment via some other strategy, and end up with a viable plan.