If I were to summarise the reason for our recent success I'd say it's due to having enough goals scorers and creators in the team. I don't want to lose that when one of our players gets injured.
This why Sancho makes sense. Sancho offers both goals and creativity. So if we're to get him we would have depth in our goalscoring and our creativity department. If we add him to our current starting 11 we would have enough creativity in midfield and enough goals in attack even with players out.
In the goals department, if we lose Rashford we play Sancho there. If we lose Martial play Ighalo. If we lose Sancho in RW, play Greenwood. Sancho, Greenwood, Ighalo, Martial, Rashford and even James gives us enough goals even when one or two is out. In the creative department, if we lose Bruno play Sancho there. If we lose Pogba play Fred there. Bruno, Sancho, Pogba, Fred gives us enough creativity even when one or two is out.
So Sancho solves two possible problems. Ideally we should be after another creator to let Sancho focus on attack but not when we have a limited budget and problems with our defensive depth. Sancho alone is versatile to solve our goal scoring and creative depth. With Sancho we can still create and score even when Bruno/Pogba/Rashford/Martial/Greenwood is out but what happens to our defense when one or both of our two key players in DM and CB - Maguire or Matic is out.
If I was to choose between DM or CB I'm leaning towards CB because Mctominay or Fred can at least do a job at DM. But our defense is already shaky even when our best defenders are on the pitch and it would even be more shaky if we were to lose our key defender Maguire.
I believe if get Sancho and a solid CB there would be enough quality and depth in goals, creativity and defensive solidity to aim for the title. As long as everyone performs that is.