The company I work for maintains and has built some custom ERP solutions. While we've never dealt with SAP directly, almost universally the mindset of the IT departments at these businesses is that they are the last defence against the dark forces of SAP.
ERP migration is a terrifying thing and they seem to fall into the same pattern every time. Company has their way (workflows, processes, strategies, philosophies) of doing things. New ERP consultant promises the tool will adapt. Company spends $50M with consultant and product trying to make the tool adapt. Pain loop of "Well, it can't really do X like we said, but we can make it do Y which is close!". Company either a) bends to the opinionated process of New ERP, b) cuts their losses and runs, c) spends years and millions more trying to fight the opinionated process and then cuts their losses and runs, and/or d) goes bankrupt.
It seems to me that the only way to do this right is to spend as much time as it takes nailing down your processes and workflows, being honest with your company about what you need to change, what you want to change, and what can functionally change. Then use the broadest technology possible and create a custom solution. I feel like there's room for a broad business logic framework/library.