Is it really a handwave to say we don't know? Sound pretty logical as opposed to just making something up or parroting some origin story like people have been doing for 1000s of years.
It's a handwave to say it's a hill climb when there's no clear mechanism to make it a hill climb. That's not saying we don't know, it's saying we DO know when we actually don't. It's basically assuming away the problem, the complexity gap between simple chemicals and systems we know can pile on complexity via natural selection.