If you can't get someone up to speed with your internal processes fast enough to at least gauge if they're following along that indicates an internal problem.
The problem is, I think, that HR does not want technical staff to see the hires for (probably made up) legal reasons. So the decision is mostly made by people who can't actually gauge competency.
"Interview was weak. They don't know what they're doing."
"Aced the interview. Fired after two weeks. Leadership doesn't know how to hire or manage."
"Never seen a place with so much churn. In the last six months, I've seen at least half a dozen engineers exit after two or three weeks."
Know what raises the level of difficulty for finding candidates? Shit reviews about the company. You can have the best tech but if you have a toxic smell, you can't hire. To the outside, perception is reality and reviews are how you get that perception. You can't do the opposite though and say "J Smith passed interview but we let them go after two weeks because they couldn't do more than pseudo code on a whiteboard." and even if you could, you'd look like a shit company and you'd still have an impossible time hiring but for other reasons.
This idea of quick hire/fire is so bad that all you have to do it go one or two steps further to find the obvious problems. But hey, start a company and use that model. See how it goes. Prove us all wrong.
I can only say that: Oh my gosh do I not want to work for a company that "hires fast and fires fast". For many different reasons.
Most people except for a few outliers will be fumbling around the first month while they learn the code and the company.
