You saw what happened when Otto, Staff and Hall were out... we had to put Vardy in the ruck. So we trade off Otto that leaves us with Staff and Hall in the ruck, what if something happens to one or both of them? Yes we have Schulz but he's not going to have the strength to go with the top ruckmen yet and won't have it for another few years. Keep Otto he had an average year last year, yes but that wasn't entirely his fault. And you can't blame him for this year in fact for someone coming back from a back injury he's done pretty damn well if you ask me.
Yes you have to trade good players to get something worth while in return but we don't have all that many big men, so unless you want a repeat of what happened in round 9 this year and all of last year, we won't be trading Otto. He's under contract anyway so we'd still have to pay him jackstar so your theory of him being paid to much may be true but at least he's playing for us.
As for who we should trade I don't know we don't have many players that'd be worth much and the ones that are we need to hang on too. Bring on the kids I guess.