imperialscum said:
Main villain could have betrayed Luke just the same and Rey could later be trained by him just the same, if he was not missing/hiding in the first place (i.e., no “finding Luke” useless filler).

Well considering Rey goes off to find Luke at the end of the film and you’d have to alter the script a bit to account for that.

Also wouldn’t getting the Death Star plans to the rebels be considered as filler too? And aside from that the implications of finding Luke are different from finding a blueprint.