The advantage in splitting up the assertions is that you get more visibility. If one test fails and not the other two that's extra information you can use to debug you wouldn't have if you have all 3 in one test.
If that test fails, the dev will just run it locally with a debugger attached. The cost of extra time in the test for the normal passing case isn't worth it.
Right, but consider if all three test cases fail. Then devs (who didn't write those tests) need to determine what those three test cases are and if they're all the same issue or not, which takes time.
Ideally, if just one assert fails, it will produce an error message/logs with enough info to tell what went wrong. Having tests produce great error messages is way more valuable than arbitrary rules about assertion density.