I think it's possible if we buy players from abroad. As you suggest in the CB position and I did above, there isn't a CB better than Smalling/Lindelof, or at least, if people rate Maguire I don't think he is a significant enough improvement to see us finish on more points than we would with the best pair we currently have. There are also obviously far better right forward / winger type players available elsewhere as well. I don't think we can poach players from Premier League teams and expect to challenge for the title, but Wan-Bissaka, Neves, Aderweireld, Rice and Doucoure are players who I think we could get and wouldn't be opposed to us signing any of them in the Summer.
However, despite me saying that, I always felt that Fergie tried to get the 'next best thing' or a rival player from a Premier League side when possible to push us on for the next challenge, so maybe it is the best way to get closer to winning the League? You can rattle off a big list of Premier League players that Sir Alex signed which improved our squad and helped us greatly in our successful periods (Cantona, Keane, Pallister, Carrick, Valencia, Tevez, Berbatov, van Persie etc).
Liverpool bought Mane and van Dijk for example and that seems to have worked. City with Stones, Walker, and Sterling has definitely been key in their title wins too.
