No need.
That can be argued.
It was made self-evident during the approach to Endor on the shuttle that Luke sensed Vader and that likewise, Vader sensed his son. There is no continuity error in the scene as it is.
And that scene has nothing to do with Luke’s sentence that creates the continuity error.
“Vader is here now, on this moon” in the Star Wars universe is like saying ‘Vader is here now in this system’. Means the same thing
Absolutely not.
It means exactly what is written. On the moon.
You can try to rationalize as much you want, on the moon means actually on the moon in every known universe. Even Star Wars universe. Because whatever they say in the movie, it is for the audience to understand.
Not in the athmosphere, not in orbit, not in the system. On the moon.
If he wanted to say something else, there are words for that.
For example Luke could have said he is coming for me.
He didn’t.
especially when trying to hurriedly convey to Leia why he must leave the group. “Here now, on this moon” is the urgency Luke needed to convey to her, so she would accept his decision to depart.
The very same thing is true if he says, “Vader is coming here for me. I must leave.”
He didn’t. He said he is already on the moon. But he wasn’t.
Besides, there is a musical flow to the editing in the sequence in which it transitions from the Ewok village to the shuttle landing. I’d hate to lose that.
Maybe the landing sequence could be placed after Solo talks to Threepio, cut back to Ewok village, then cut to the part when Vader exits the elevator.