Arbitrary filtering of candidates doesn't reduce the effort that it takes. Let's say 1 out of 1000 of the candidates you see is what you need. The total amount of effort to find the right candidate is still the same. But throwing out half the resumes just doubles the amount of time until you find the candidate you need (you just spread lower effort over a longer time).

On the other hand if you "raise your bar" (let's say you do so by some method that makes it twice as expensive to judge a candidate; twice as likely to reject a candidate that would fit what you need, i.e. doubles your false negative rate; but cuts down on the number of applications by 10x, so that now 1 out of 100 candidates are what you need, which isn't that far off the mark for certain kinds of things), you cut down the effort (and time) you need to spend on finding a candidate by over double.

EDIT: On reflection I think we're mainly talking past each other. You are thinking of a scenario where all stages take roughly the same amount of effort/time, whereas tmorel and I are thinking of a scenario where different stages take different amounts of effort/time. If you "raise the bar" on the stages that take less amount of effort/time (assuming that those stages still have some amount of selection usefulness) then you will reduce the overall amount of time/energy spent on hiring someone that meets your final bar.

Some more thoughts before I go to bed.

This could also be used for combating spam elsewhere, like posting in forums, comment sections and so on. To preserve privacy, something like zero-knowledge proofs could be utilized. I don't know how the cryptography would work exactly, but if you can't double spend a credit and you can choose whether to keep it anonymous or not, it could work, too. It would be best if for a given credit spent, you could only disclose your identity to the entity you want access to, not the credit issuing entity.

For spam, it seems like the cost of maintaining a forum like the servers are much lower than the cost of the mods that deal with spam. So instead of paying the forum directly, we lower the need for human mods to spend their time. That way we lower resources to the forum indirectly. The credits could be per post or per account creation. I assume the HN mods' time is worth a lot more than the servers and power HN runs on.

Also, we won't have the issue that PoW and other proofs-of-X's have of being easier to do on some devices, but harder on others (like the power and time it takes to run PoW on a beefy desktop with AES-NI vs an on old phone).

But we'll still have the issue with different standards of living in different places making the credits more or less expensive for the user subjectively. Companies hiring worldwide could require different amounts of credits for applicants from different countries, but for forums this wouldn't work.

A solution to that could be issuers giving credits for local volunteering work. Clean up some garbage from the shore and get a credit regardless of whether you're in the USA or Bangladesh. But if you want to prevent credits from being traded (do we? idk) and, at the same time, have some amount of privacy, how would you do it?

But now you'd have to make sure that credit issuers all over the world only issue credits for real charity-like work. And who's to say how to value picking up garbage vs volunteering at an animal shelter vs donating 1$ to a charity.

It's interesting to think about this, even though I don't have any resource to implement anything like that.

Professional certifications have a terrible reputation for good reason. You are perhaps too young to know why this is a silly idea. But its been tried and it failed spectacularly.