I understand your reaction. I'm sorry if it comes across as one.
I'm not too worried about it. It's unlikely they want to do map much harm. With new mappers it can be discussed eventually if needed. They are likely to get a welcome message from us and learn about this regardless. Corporate mappers should adjust to the organized editing guidelines, and it can take a bit before they cooperate. For more experienced mappers -not to be all personal about it-, it'd be good courtesy towards fellow mappers. It makes it easier to verify other mappers' changes and discuss their edits.
https://wiki.openstreetmap.org/wiki/Verifiability

I'm aware the changes you are doing are not changing much, they're more reverting incorrect changes. Still, it'd only be reasonable to use the local sources which the local community has agreed upon for best practice.

I hope this helps to clarify things.