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).
I believe Real Madrid can reach a higher level with Alonso. Their rivalry with Barcelona in Spain will continue. Atletico Madrid is another Spanish team that could challenge them, but Xabi Alonso is a manager who shares his genes. He knows exactly what the team needs and what they need to do. I have complete faith in him and believe they can succeed this year. If they can establish a good balance of power among their star players, I think Real Madrid will have no problems. Carlo Ancelotti had trouble with this. From what I've seen, he's been overly tolerant towards his star players.