> But if you ask them about other _still fundamental_ knowledge like a _rough_ idea about what the different transaction isolation level are/mean/imply for you, they fail hard.

More a property of concurrency than of SQL, I believe; your point applies for programming languages too.

It's possible to get by as a programmer with no real understanding of how concurrency works in the relevant languages.

If concurrency bugs were always obvious, doubtless things would be different.