There are a few things needed for that to be a good argument 1) Their security really is so good (I'd bet it isn't. I saw a tenured security professor/former State Department cyber expert get phished on the first go by an undergrad.) 2) Google isn't improving their security posture on top of that (I'd be shocked if Google isn't improving theirs, and I'm certain having JS required to sign into gmail closes a major hole in observability of automation) 3) There are real harms from the JS being there for their security/privacy posture (as I've said elsewhere, I'm unconvinced Google is allowed by their own privacy policy from doing anything untoward here)
As to your point about computer literacy and existence, I think the sad truth is that computer engagement is required, but literacy is optional. When that's the case, large companies are in the position of having to defend even the least computer literate against the most vicious of attackers.