Yes, they vary widely. With a vast majority of cases being trivial, simpler-than-textbook, and the rest mostly suitable for a nice and clean split between the C.R.U.D. workflow part and all that complex logic you're talking about, which is also usually being implemented by the idiots in a most unsuitable way, using low level languages and no proper abstractions.

And yes, ERP is a pile of stupid shit. But you need an army of morally deprived Oracle-style salesmen to sell shit to the world. I know it well, worked a lot with the Oracle "partners" in the past. Oracle is a synonym for "overengineering".