That sounds like hell. I need to meet the team I'll be working with before accepting an offer. It's the only way to know if they're competent, can communicate, and are not assholes.
This is exactly how Facebook's onboarding process works (at least in engineering). You spend 3-4 weeks in "bootcamp" classes (React 101, IOS 101, etc.). After that, you spend another 3-4 weeks auditioning teams -- you sit with teams that have open headcount for a week, attend their meetings, and work with a mentor on a coding project. Once you decide which team is the best fit, you "graduate" bootcamp and join them.
It's not perfect -- if there's no open headcount on your dream team, you'll have to pick another, but it's the best onboarding process I've seen from an employee standpoint.
Is this a significant fraction of hires? Because I find it really odd to waste the time of a say an embedded software engineer trying to teach them React when they're pretty set on working on something else anyways…
Good question. It's definitely not just for new grads (I went through team selection as an IC5/senior engineer). There is a process where you can be hired directly onto a specific team, but I got the impression that it's the exception rather than the rule.
I would guess that someone joining at a super-high level like a principal engineer would be doing so to work on a specific team or technology.