I didn't say "just write better code", I said write more tests. Writing those tests will produce better code.
I also never said unit tests were the ONLY tests.
But you were ONLY talking about unit tests for catching concurrency bugs; bugs which often fall outside the scope of a unit being tested.
Nobody disagrees with your point about the importance of unit tests. But the way you present that point is more than a little naive (and that’s the polite way of putting it).