So, I don't want to sound snarky, because what you are saying is not false, it just misses something. The nist compatibility guidelines aren't just about syntactic guidelines, they are about checking to make sure the isolation levels work correctly. The tests are meant to be extensive and reproducible. I'm not saying they are perfect, but I would suggest databases have been testing these particular issues for a long time. Another good tool to checkout is jepsen. Anyway, Nist compatibility guidelines are underused and as a result open source databases miss out.