I absolutely agree that there exists terrible code and that there are incompetent individuals or folks that simply don't care. But if one assumes that as the default response, I don't think that is very helpful.
Even in your example of shared data/synchronization - what if the original developers were told that the code would never need to be thread-safe? Or what if there was a constraint that required this trade-off to be made? It's not so black and white.
Hell, even incompetent looking code (like managing shared resources poorly) can often be explained by a small script done by an amateur turning into a side business and then a full fledged company. Experience and knowledge of an industry beyond software is often many times more valuable than the knowledge of parallel programming. It doesn't mean the code wasn't valuable or good enough at the time, it just no longer meets the rigor and demands, that's why you're employed to work on it. To call everything shitty thats's below your own standards, level of education and experience is a naive view of how software actually exists in the world. Especially when the standard advice given to "idea people" is to learn to code their idea themselves.
It is helpful. It gives you the confidence to change things. It allows you to feel productive. And it's true often enough that it's a reasonable default, IME.
That seems like a dangerous way to feel confident in your own work and abilities to me. Pinning your self worth to comparisons with others is not so helpful, long term, as you might think.
Even in your example of shared data/synchronization - what if the original developers were told that the code would never need to be thread-safe? Or what if there was a constraint that required this trade-off to be made? It's not so black and white.