You've got some reasonable points and I don't just want to completely gang-tackle you here, but there is a part of your argument that I think is sufficiently incorrect in a sufficiently harmful way that I'm going to sort of keep at you about it, in what I hope is an open-minded or at least respectful way.
Some people like the book "Coders at Work" (I do), some do not, but almost anyone would agree that the people interviewed are absolute luminaries [0].
There are 15 chapters comprising 15 interviews. You have to get to #6, arguably #7 before you find someone who at the time of writing wasn't both a world-renowned hacker and currently or at one time a demonstrably successful engineering leader. The first 5 being: jwz, Brad Fitzpatrick, Douglas Crockford, Brendan Eich, Joshua Bloch. It starts to get a little blurry in the second half because it's so thick with CS academics (who in a different way also do engineering management), but you've still got VP-types who still code like Peter Norvig. The ~50% who aren't demonstrated engineering leaders are super hard-core CS researchers like Donald Knuth. The book doesn't even interview Cliff Click, or John Carmack, or talk about the fact that Larry Page and Sergey Brin wrote the first version of Google themselves and continued maintaining parts of it well into hyper-growth. Eric Schmidt wrote `lex`. When Jack Dorsey was recruiting me for Square over lunch he made an incredibly eloquent argument about why he uses OCaml rather than Haskell for his personal hacking.
At the time I was an L7 EM, my L9 boss didn't have much time to write code, but asked probing questions about everything from the merits of various binary classifiers given imbalanced underlying Bernoulli distributions to the algebraic properties of the data structures we were using for distributed systems convergence.
I don't dispute that plenty of successful leaders in technical organizations have become rusty as hackers when they hit the mega-seniority, but the idea that some L6/L7 manager shouldn't be able to lift some of their team's serious code off the ground, let alone some undergraduate dynamic-programming interview question as was the original point of my original post is simply contradicted by a mountain of evidence both generally-available and anecdotal to numerous people in this thread.
You can get ahead as a mid-level EM without knowing the frib-frobs from that whatsits, but God-willing I'll never work for one again. That's a visibility game, it's a popularity game, it's a schedule-too-many-meetings game, it's a post-too-much-on-the-internal thing game. Fuck that game.
[0] https://www.oreilly.com/library/view/coders-at-work/97814302...