ETH's win percentage of 74.1% in all games since he joined United is typically more than enough to win the league in most seasons. Arsenal have just had a ridiculously good run, although I fully expect them to self implode over the second half of the season.
Fully agree that Kane and a top CM are the two key additions, and they would also by definition provide more depth as well. Eriksen and Martial would replace Fred and Mcneill(?) As the first change in their respective positions.
In the second half of the season, the team with the bigger squads and more strength in depth have the advantage. Arsenal's second XI is really quite weak, but City only have a small drop in quality from their first XI to their second XI, e.g. Haaland to Alverez is a nice problem to have.
Our first XI is comparable to either of City's or Arsenal's, and our second XI is probably somewhere in between, but with ETH's superior management skills, who knows....?