Being able to quickly understand and debug a large vertical slice of a system across many layers like that without docs or handholding is really valuable in a broad SRE/production engineering type role or a do everything early engineer type role when docs/handholding are in short supply.

Not to say you have to have it. Many engineers are bad at this but way better at consistently putting out solid bug-free code quickly than me and thats a huge chunk of engineering as well.

But it is a learnable skill. 90% is honestly just reading errors carefully, googling them and following the trail but many people have sort of a panic/ignore response when a weird looking error messsage comes up somewhere and interrupts the flow.