And yes, it is a very obvious point, and that people keep missing that point on this site is unsettling. (Also, yes, this can be trivially circumvented if you just let those people program, instead of only do verification.)
You can, also obviously, replace millions of average developers with (way more) millions of extremely competent spec writers if they can use formal methods. Those will require way more computing power than it can ever exist on Earth to do their work, but they can mathematically get there.
Why do you think you need orders of magnitude more spec writers than coders rather than the other way around?
AFAIK, those are the only ones in common use, but differently from formal ones, non-formal things tends to come on a multitude of widely different types. So I wouldn't be surprised if people have invented many more.
Gonna be really fun when the first financial companies start trying to generate billing software from specs and end up blowing up entire people's bank accounts irrevocably because of lax regulation and greedy shareholders. Not to mention that any resources you trim from the developer side of things you'll have to at least quintuple in QA.
Formally verifying it will easily take more computing power than training the AI on the first place, so I don't count that one as viable.
Or just use English and do lots of acceptance testing plus add fail safes. I bet that will be more economical.