Jane Street likely has the highest applicant to available role ratio of any company in the world. I'm sure some heavy filtering is required, and probably useful.
We should also remember that Jane Street is primarily an ETF market maker. Their main business isn't betting on prices of stocks or managing a portfolio.
I've only taken a quick look at the data, but the problem doesn't seem to be focused on their core competencies, but instead is much more general.
2nd paragraph starts with: "We used Claude and Allium"
And later on: "With that obligation written down, Claude traced every path that runs after gyros_busy is set to true"