That's why I think as long as you have documented and defined your methods (i.e. business logic) well, and your data is portable, you shouldn't worry much about

That's why I think as long as you have documented and defined your methods (i.e. business logic) well, and your data is portable, you shouldn't worry much about vendor lock-in in the long run. That's a huge big IF. In many if not most cases the only reliable documentation of a system is the running code itself.