I know that Ben's ghost scene isn't much of a retort from Luke but it's all that we can get and just having Luke stumble on the truth at some point isn't something that can be done with the existing material.

If Lucas had done it properly we we would have shots of Luke noticing Skywalker style behaviour and then we he tells Leia (or even when he second guesses Ben's ghost in the existing versions) it could have been a semi-plausible revelation but then if Lucas had been in a mind to do it properly Leia would never have been the Other in the first place.

Leia does show Skywalker style behaviour but he's hardly ever around when she does it, (choking Lando via Chewie, choking Jabba, rushing in to save Han, sensing Lando isn't quite right etc). If anything Luke is more likely to conclude Han is his sister going on the evidence he's around to see.

If Luke had been around to notice these things at least Ben could then argue he was trying to protect her from herself and that Luke showed less potential for going the same way Anakin did.

So if we have to have the Ben scene (and I fear we do) putting him on Tatooine where he has a strong connection to Luke makes more sense, to me at least, for all the reasons I've listed.