The thing is that there's no way Sydney would trade him. Given they only have 1 accomplished ruckman in Pyke, Tippett is probably the most important person in their side, structurally.
Tippett is the player that every club in the AFL needs, he's the only Ruckman in the AFL who would get a game purely as a key forward even if he couldn't ruck, and as a ruckman he's not too bad either, wins his fair share of hitouts.
Having Tippett allows you to run 3 genuine key tall forwards in the team without sacrificing anything, which would stretch any defense.
If you were picking an All-Australian side that actually had to play against another AFL team, you'd pick Tippett as your backup ruck every time, knowing that he'd only be rucking for about 25% of the game and spending the rest of the time forward.