That sounds like JS developer mentality where you rewrite everything in a different framework every year so figuring stuff out in-depth is a waste of time and you just duct tape everything to get it working.
Ephemera and arcana I've learned decade ago still serve me well today, even when it's outdated people mostly either reinvent stuff so I can recognise new stuff as a variation on an existing thing or build on previous solutions so I know the details and circumstances that lead to some developments and this lets me understand new things better as well (puts it in context).
>Ephemera and arcana I've learned decade ago still serve me well today,
I think the usual back and forth about developer interviews may have this thought as an underlying assumption; specifically people who can solve a red/black tree on the whiteboard at the drop of a hat must be filled to the brim with useful but potentially obscure knowledge. (Obscure to those who haven't majored in CS or a related field.)
It would be interesting to submit an ask hn "What is your so there I was doing x, y, z when being able to answer obscure interview question seventeen saved the day" story.
(That's not well worded but you get the idea).
Ephemera and arcana I've learned decade ago still serve me well today, even when it's outdated people mostly either reinvent stuff so I can recognise new stuff as a variation on an existing thing or build on previous solutions so I know the details and circumstances that lead to some developments and this lets me understand new things better as well (puts it in context).