Real Madrid is a big team, so it's natural to expect a coach who can deliver success quickly, but it won't be easy for Xabi Alonso.
I think Madrid is a unique case tbh. You need to win things asap because the fans and boards are not happy if you fail, whatever the reason is. I think that's why Ancelotti is loved. I think other big clubs have some leeway (1-2 seasons) for a new manager to fix things and rebuild the squad unless they're doing extremely stupid things like playing GK upfront or something similar. Well, hopefully things change with Alonso (although that seems unlikely).
As Real Madrid fans, we naturally want the team to succeed, and many would be unhappy if Real Madrid went trophyless that season. But with the change in manager, I think it will take a season or two for the new manager to adapt. But a team like Real Madrid is different from any other. Real Madrid is one of the best teams in the world, so it's natural for fans to want at least one title every season. With the current squad, Real Madrid should have overcome their defensive woes from last season. I can't wait to see how they avenge their loss to Barcelona the previous season.