That's not necessary either. What we're talking about here is an analog for the real problem, which is "when using an object oriented language, write pure functions even though the language doesn't make you do it".

Static functions introduce friction against making impure functions, but not an overwhelming amount of it. If it's all you have, then there are worse safety blankets, but it's not going to solve your lack of buy-in problem. If everyone is on board then you don't need static functions. If they aren't, static functions aren't going to save you, they're just going to extend the amount of time you suffer before you wise up and get a new job somewhere else.