If it's enough for you to say that because you have a test that everyone takes and it filters your candidates so that's proof of ability, without even going into the results and asking if your test is optimizing for the correct things, there's nothing I can say to convince you otherwise.
Anecdotal, but I know about a half dozen people with experience and CS degrees who would blow your filter but can really get shit done and don't really need any training.
Hiring is hard and the real shame of this industry is that collectively we don't approach this problem with the same level of rigor that we do everything else because by and large we consider this sort of work to be beneath us and not worth a significant investment of our time.