I think the original direction was to have Luke start as ignorant of even the existence of the Force and eventual move up through difficult trials until he was in the position to train his sister in much the same way young Obi-Wan would have trained Vader and then would come the uncertainty as to if he would make the same mistakes or not and lead to the fall of the Empire or making it even stronger.

The whole literal resurrection of Ben and Yoda business was a bit too weird and took away from Luke being the main focus of his own character arc but something had to happen to push Luke away from the comfort zone of the trinity of Luke, Leia and Han to further push his character up to the next level.

It is odd however how much Leia being Luke's sister retroactively makes sense (probably more than Vader being his dad to be honest even with the kissing).