Can you gain deeper understanding without first gaining superficial understanding, though? And if not and our current method of imparting superficial knowledge breaks down, wouldn't there be a pipeline problem because much fewer students would get to the point where you can start teaching them deep understanding?

(Imagine a scenario in which no assessment is possible in any mathematics course below the level of differential geometry. Would "we just have to switch to teaching students advanced math instead" be a solution?)

Something along the lines of this is already a problem at US universities, as students chegg, stackexchange and collaborate their way through up-to-junior courses and then are so underprepared in senior-level ones that really 80% of a given class ought to be failed if this were politically feasible. At least though the current situation is more due to a lack of will than a lack of way to stop the cheating, so students are under some pressure to not make it too egriegious.