That feels like a lot of nitpicking, and I’m not sure if it’s really valid. The whole point of that scene is that the audience can’t be sure if Palpatine is telling the truth. He’s manipulative, what he says to one person can be different from what he says to another. He acts like he doesn’t care about Luke, but in reality he’s afraid. He knows the light is more powerful than the darkness, and tries his best to eliminate the closest threat to his power. But he didn’t realize that the closest threat to him was his own second-in-command. Him not realizing that Vader will betray him is a key plot point, it’s not a hole in the story or anything like that. He claimed that Luke had a lack of vision, but in reality he was the one who couldn’t forsee his own demise.