Agree, except one point. You adapt your system to SAP, not the other way round. And tgat is actually a much better thing than it seems, because SAP is used in so many comoanies that you get a load of best practices out of the box. Adapt those core competitive advantages you have, take the rest as is.
By the way, edge cases, if if they work in a legacy system, are a thing to get rid of during a SAP / ERP implementation. Most people see ERP systems as IT projects and fail. ERP projects are at least as much business reengineering projects as they are IT projects.