Not in the NFL they don't. Name 5 players that successfully went from either LB to S or S to LB.
Moving from CB to S, or S to CB is completely different.
I can't name any players off the top of my head that were successful at the SS to LB move, but I can name some that made the move. But my point in the post you quoted was about position changes in general.
So your first point about "Not in the NFL they don't" isn't true. Yes they do.