That’s correct.
Wouldn’t copy/paste though.
Just insert a full template and delete what’s not needed.
But that’s totally up to you how you proceed.
A one-click solution isn’t available for this, but that’s not required for one-page templates in my opinion.
It is planned to add themes, which then automatically creates everything needed (templates, template parts, fragments, pages, etc).
I think that’s exactly what you are looking for.