An issue with removing Banner of Command
Banner of Command was strong. We all can agree to that. Baron made it too OP, and after a while, it was removed. However, one of the various situations which for Banner of Command, was a perfect fit, no longer has an answer. That is split-pushing from behind.
Banner of Command was the bane of all AP champions. In other words, many champions with a lot of wave clear. So split-pushing a wave was a great use for it. You could place it bot and still contest baron while the lane pushed if you were behind. Zz'rot Portal at most just freezes it. But Banner actually pushed it, even if your team was behind. As long as super minions were not facing it, it could shove any wave at least to the tower or for quite a few waves.
I think that just reverting the Baron buff or other OP changes would have been a better option.