In larger corporations it may not be 100% finalized where you would end up.

Knowing that yes, you master compilers (that's usually quickly determined, potentially fast enough for you not to notice it since you live and breath compilers), have basic knowledge in smashing together enough html tags to build a simple dashboard but you never had to deal with processes that spanned multiple computers, allows more flexible allocation:

Ideally, they'll give you a compiler related task, but if they find someone even more suited for that one open position in compiler internals, they might offer you a job in the adjacent compiler-as-a-service team where you'd start out doing dashboards and then move to whatever more complex task needs work.

But they won't need to bother offering you the distributed systems position that scales up the compiler-as-a-service product across the whole world without sending you to some training first.

I’m not going to take the job if I don’t wind up in a group working on problems that interest me. That is part of the bidirectional interview right? I hesitated even applying to a big Corp until a few people there convinced me they had problems right up my ally. I don’t want to work at big corp just to be working at big corp!

The hiring pipeline at every big company I've been at is not always the same. Yeah, part of it is always just a big funnel that takes general applicants in and assumes they might end up anywhere in the company. But, there is also going to be a way for specialized teams to hire specialized candidates. If you find yourself in the big funnel, by all means, just tell them you aren't interested if that's not what you want. If you want to work on compilers, you need to find a way to get into the pipeline for a compiler team, and that's not really much different than finding a job with a small company.

Yes, I already did this with Amazon who hires for specific roles, but the recruiters I’ve dealt with seem to be into bait and switch (substitute very appropriate role I applied for with something completely inappropriate).

The job opportunities are definitely out there, but many of them really require a referral (the JDs aren’t posted), and even then you might have to do a generalist interview because the company is not capable of doing anything else.

Because at big corps engineers might get assigned interviews as a routine work. And any engineer has their favourite questions that they know the answer to. They dont want to take.the extra effort and come up with new questions just to adapt to your profile or expertise. It goes the other way around. I.e.the interviewer is not going to do.extra work to validate the candidate but the candidate has to prove him/herself. Take it or leave it.

The one size fits all interview at a big corp is game-able at least, with plenty of practice material available online. It isn’t a huge hurdle if you have a month or two to practice, but that makes the whole process even more questionable.