No 1 player is going to win us the title. You need to get that out of your head. Sign Koulibaly at CB, and we don't win the title with our depth in attack. I'm looking towards the 2021/22 season personally.
Sancho doesn't need to win anything to be classified as a 90m player. He's classified as a 90m player because he's just had his age 18 and 19 seasons with ridiculous end product, with great dribbling stats, and is ridiculously skilled. He was an elite prospect prior to going to Dortmund, which is the whole reason why Dortmund bought him in the first place. He's not some unheard of player who Dortmund turned to gold. They gave him playing time, which is what he wanted at City, but didn't get promised. Dortmund should get credit for that, but to take all of the credit would be strange considering how highly thought of he was prior to his move.
To put this into perspective, when was the last time we seen an 18 and 19 year old put up his end product, with his dribbling ability, and with his technical skill in any of the top 5 leagues? In the Championship? In Eredivisie? So if I lower the standard in league, meaning that I include more than just the top 5 leagues and cast a wider less exclusive net, you still struggle to find that sort of profile in a player. This highlights why he's worth as much as he's worth.