That was sort of my company's IT story.

In the beginning they needed AD because business is heavily Windows centric.

Then they started using Windows Server for DNS, business apps, shared volumes, etc...

After I joined I started separating concerns / reducing blast radius and now we use Windows Server for AD and a few apps that are Windows only.

Azure AD + Intune MDM is getting better and I think we will be able to kill our managed AD soonish though.