Gueye isn’t a center forward, he’s a roaming 10. You saw today he was central, wide left, and a couple of times out right. He’d do more damage than good at 9, wouldn’t play his position centrally and, in my opinion, would get in others way out wide and deep. Doesn’t have the discipline for 9, he’s is that free roaming creative type.
I think he’s a deep lying center mid, very much like sivert. Play them both, do they get in each others way and prevent each other from playing their natural game? Would like to see palaversa and shinnie with gueye ahead of them at 10.