I spent the better part of a year and a half writing automation for an integrated stack that included D365. (RSAT wasn't an option since we had to also interact with other systems and sql databases and what not to perform end-to-end flows across multiple systems.) It was literally the biggest resource and time suck of all the stuff we had to interact with -- and we had to interact with some really hoky stuff. But D365 took the cake. At least two people quit over it.