Spicy take: they would’ve had to have used Ewan McGregor to have his ghost appear in TROS, and I wouldn’t mind that option if Jonh ever decides to waste his time blessing us with more variants. Yes, Luke only ever knew old Obi-Wan, so it makes sense that that’s how he appears to him in the OT and ROTJ, but Rey knew none of them and she hears Ewan’s voice 90% of the time when she hears ghost Obi so that’s not really a factor here.

Edit: whoops, this isn’t getting back on topic.