It's not clear to me that Guardiola was in for Sanchez. I know that that is contrary to prevailing opinion, but I don't think we followed up on this Summer's interest until the injury to Jesus, and then when we found out the terms required, the interest ended there and then.
If you look at the City team, there is no role for Sanchez other than as cover for Aguero/Jesus. He's too slow to play wide. He can play in midfield but we have specialised midfielders who can do that. Utd's team rebuilding is far behind City. They can probably make more use of Sanchez than City can, but I don't see it as a transformative signing.
I doubt sanchez will strike fear into the defence of City, Chelsea, Spurs, Liverpool etc