Safety critical software is about limiting the available software constructs to known safe ones (eg the MISRA standard) and adopting techniques and tooling like

Safety critical software is about limiting the available software constructs to known safe ones (eg the MISRA standard) and adopting techniques and tooling like TLA+ that can be used to prove correct behavior. Things like FMECA etc are techniques for safe software (and hardware). Diagrams don't replace that. OOP as a technique (at least stuff about classes and inheritance and polymorphism) doesn't replace that. OOP in terms of objects and messaging, with state machines are certainly part of safety software development. The leftover CASE tools like Enterprise Architect are now basically documentation engines and have very little to do with the actual software development process.