I'm a pre-Millennial engineer so I've been around long enough to know that the default tech interview system is pretty much broken. So much of interviews are focused on stupid college homework coding questions even for folks that have been out of school for a long time. I'm guilty of using those too, but I'm reforming. Granted, such questions have more value for newly minted college grads.

You can learn much more about a candidate by asking them to bring in work samples or slide decks showing off what they've accomplished. This will uncover MUCH more about their personality, work ethic, public speaking/presentation skills, ability to convey technical information in a concise manner, creativity, how they do as part of a team, what they value about their professional and educational experience, and where they'd fit in your team.

Also, are you one of the sucker employers who fall for the schmoozing, job-hopping type? It sounds like you may be. I've seen these types over the years. They're smooth talkers who are expert at acing interviews and wowing the gatekeepers but hop from job to job looking for the next bump in paycheck or title because they don't actually have the work ethic to stick around and finish what they start. They have to move around because the boss eventually figures out they are all talk.

If you've fallen for this, you should try giving a chance to the next guy you interview who is humbler, can't quite answer all your questions the way you'd like, maybe things don't click as well in his mind under pressure or being on the hot seat makes him forget what he truly knows because he suffers from test or performance anxiety.

These types won't sound as impressive on paper or in person because they don't oversell their abilities, but are honest and transparent about their experiences and strengths. They do much better on take home tests where the pressure is off and they can think. They might be quiet or reserved. They might not know everything you quiz them on, but they express an eagerness to learn. They're grateful for the opportunity you offer, because they usually get passed over in favor of the aforementioned schmoozers. It can be counter-intuitive to hire these guys but you might find a hard-working, productive employee inside.