I've worked in both scenario's centralized RPA while other smaller automation functions were left to the business unit, as well as having it all centralized. In a smaller environment, centralizing it to a core team makes sense and is fairly easy to implement and control. In a larger environment, controller the usage of automation tools, and centralizing may become a bottleneck, as there are just too many demands and complexes for a single unit to understand.
I would recommend RPA long term due to it's major reliance on the GUI. In theory you can MVP with RPA for a period of time until you have a more elegant solution leveraging for example an Azure pipeline that can trigger some of the actions needed on AD and other systems.