Pull-ups, campusing and Bacher Ladders are all completely different, with pull-ups being the most different.

On a ladder or a campus board, you are moving up and down the rungs. Naturally, there is dynamic movement involved. The stronger you are, the better you can hold a one arm lock off, the less dynamic the move. But then you are working on one arm lock offs which is something else that a pull-up doesn't work.

A campus board also works finger strength and to counteract the fact that the rails are tiny, it is a bit less steep than a Bacher Ladder. There are different types of finger strength and I don't know which a campus board works best but it's not necessarily the same as a hang board.

Ladders and campus boards mimic climbing movement, while a pull-up is just a pull-up. There are often times when you need to do a one arm lock off and/or a dynamic move in which you reach with one hand and this is why ladders and campus boards train you to do so. Moving down on a ladder or campus board is using the principle of negative resistance, much like weight lifters do when they train.

There are never times in climbing when you need to to a pull up, hanging from both arms and raising your chin above the holds. What would be the point of that?

What does work for climbing in terms of pull-ups is to do offset pull ups. Double a towel over your pull up bar. With one hand hold the bar and the other hold the towel, about a foot under the bar. Do sets, switch hands, etc. This begins to train you for one arm lock offs, and is not as intense (or effective) as campusing or ladders.