I don't think Nuno is that bad of a manager. Is he great? no. Was there better out there? Maybe. But who was taking that job? It's not like there was a queue lining up for it.
They also bought 5 players (most of whom are expected to be key cogs), and sold a boat load. That type of turnover takes a lot of work to integrate. Probably more importantly, who they didn't sell is clearly dragging that club down. Kane wanted away, stomped his feet, and he's still there. That's a locker cancer that many managers are not ready or equipped to handle. Especially of his caliber and level of player. It's one thing if a mediocre player wants to go. You can bury him in the stands. Harry f'ing Kane is that club. If he's not happy, they're going to show it.