I think Rian interpreted Luke in about the only way he could given TFA’s setup. At least the best way one could if they put more than 45 seconds of concerted effort toward.
Actually, I think the lack of screen time Luke has gives even more possibilities as to why he ran away. Just going off of TFA’s previously mentioned setup, I can think of some stuff already:
- Luke searched for the ancient Jedi texts in order to find a way to redeem Ben.
- Luke sensed that Ben’s turn had been caused by some unforeseen threat, and searched for the ancient Jedi texts in order to find a way to stop it.
- Luke’s exile was purely caused by guilt over Ben’s fall, nothing related to wanting the Jedi to end.
Those are just some ideas, but I could probably think of more. Either way, “time for the Jedi to end” was certainly not the only way they could have motivated Luke to exile himself.