I’m not sure I fully agree. There are plenty of good positions (at least in Europe) where they ask for an engineer who can work with tool/Lang x, and won’t ask

I’m not sure I fully agree. There are plenty of good positions (at least in Europe) where they ask for an engineer who can work with tool/Lang x, and won’t ask you to invert a binary tree, but will ask you about what kind of projects you’ve worked on. I thought that was what you meant by #2, until you mentioned that it required “really prolific” engagement with open source.