I hear that it would take the effort of cutting and pasting a few lines of code to tighten up this test. So, what kind of super strong need could justify that cost in human misery?
What is the need to do a better unit test when there are already better redundant upstream tests -- that's just like asking what is the need to have ANY unit tests when there are redundant upstream tests. Answer: -- it helps to (better) isolate the failure.
Picture a bug that fails the higher level tests but seems to have passed the very similar unit tests -- doesn't that sound like a bug in the exception propagation code? How much time down that rat hole would have to rack up before it amounted to a super strong reason to have taken some simple advice while the trail was fresh.