Sabitzer is the kind of midfielder we're going to need during the nine month ordeal commonly known as a football season.
Think about it. Bruno and Casemiro are our untouchable midfielders, but after that the drop off the cliff is a bit steep: Eriksen, Fred, Donny and Scotty. A fit Eriksen is a great asset for us, but he's no longer a 2x/week midfielder. Fred, Donny and Scott? Need I say more?
But what abount Mount? A clear upgrade on Eriksen, so with Eriksen as Mount's cover we'll be alright there. But we're not going to get through an entire football season with four midfielders. Sabitzer is no masterful 10, 8 or 6 but in a pinch can do any of those jobs. Unless the transfer fee and/or wages are out of bounds, we might do well to offload any two of Fred/Donny/Scotty and keep Sabitzer while we add Mount to the squad.