Eh I get that you’re excited about Rey redefining what means to be a Jedi but isn’t that exactly what Luke did/was expected to do post-RotJ??? I mean, they literally picked his character arc, re skinned it and just gave him anew character arc to fit in with the new Luke. So, in a way, Luke’s also just plot device. Only in a way though.
That’s not entirely true. Yoda wanted Luke to ‘pass on what you have learned’, implying that the Jedi would come back, or return, as they were before the purge. There was no talk of ‘redefining what it means to be a Jedi’. In TLJ, Luke explicitly states that the Jedi should end, and specifically avoids teaching Rey the rules and dogma of the Jedi. She really is free to make her own way.