If the FDA was not so strict in requiring evidence, medicine would look like the supplement aisle, and the incentive to actually do the stupidly hard work of developing effective drugs & proving their efficacy would disappear.
Why even bother investing in developing a complex new antibody if you can sell some mushroom powder from a beach and claim whatever you want about it, ala Tim Ferris & "BrainQUICKEN".
There are plently of valid "incremental" critiques about the FDA. IMO, their devices and diagnostics divisions are weaker than CDER and CBER. Even those two (drug focused) divisions can be too slow moving and occasionally capricious about when they want more evidence. But their final decisions are generally pretty good, with a few exceptions. And most of those exceptions are drugs that they approved that they shouldn't have (e.g. Aduhelm) - not vice versa.
Can you point at a promising drug candidate with statistically solid efficacy data that CDER or CBER has rejected?
Also - note that there are approved scFVs and VHHs and mimetics - as stated in the article. Each is useful in particular situations, but none is some sort of wild medical breakthrough. There is just no evidence that any of these modalities would be attracting extraordinary investment "if only it weren't for the FDA".