This isn't really accurate of Jane Street. As the other commenter mentioned, it's not a hedge fund. Secondly, engineering culture at JS is typically the opposite of what you described. A lot of time is spent to make sure all code written is quality, things move slower than a company like Facebook for sure.
> Best in class engineering and internet scale problems? Nope
This is mostly true apart from a few specific teams and projects. I think most passionate engineers would find the work uninspiring.
Sorry, I should have said "trading firms", but they are pretty similar culture wise. Most hedge funds have internal funds as well and they run it similar to a prop trading firm.
I think in general though a small company (JS has 900 employees, so I'm guessing around 50-100 devs) simply can't hyper optimize their entire engineering stack to the same extent that a large FAANG can. It's far too wasteful. And I'm talking about tooling, infra, and overall process, not just the code. Code review is the minimum any competent engineering org should be doing.
There are significantly more devs than that (the total is also over 900, that's from 2018).
It depends what you mean by "optimizing their engineering stack". They certainly do put a lot of effort into tooling, by necessity since historically there hasn't been much available for OCaml. For an example of stuff going beyond the open source work to make OCaml usable for large projects, see https://blog.janestreet.com/putting-the-i-back-in-ide-toward...
Obviously there is a lot of infrastructure that you need at a FAANG and not at a company with a few hundred devs. But any trading company that doesn't want to pull a Knight Capital needs to make sure their software is correct and reliable (probably to a greater extent than most of a FAANG).
> Best in class engineering and internet scale problems? Nope
This is mostly true apart from a few specific teams and projects. I think most passionate engineers would find the work uninspiring.