Sancho was the best option to play off of Ronaldo. Then it became apparent Rashford was being shoehorned for his vertical threat/pace. Rashford doesn't make good decisions nor is he a natural service provider. He skews heavily on final product. Then there was a better balance of Sancho and Elanga, with Ronaldo.
And while the club does need a left footed attacker, I will disagree on a front three of Rashford, Sancho, and Antony being very very good.
If Ronaldo, Rooney, and Tevez was an elite fluid front 3...compare that to what you just suggested, in terms of what is needed from them as individuals and collectively.
Sancho and Rashford are below average headers of the ball. Rashford isn't a good short to medium passer nor does he connect/link play that well. Rashford at his best is the only proven goal scorer of the trio. Rashford is very 1 footed and seems to be the same for Antony. Rashford doesn't have the spatial recognition or instincts compared to Sancho. None of the players have shown any proper striker instincts around the goal area to position themselves (inside 12 yards) to be of the requisite level.
While agree Antony is a type of player needed, there must be a large improvement on Marcus's part, plus the understanding of how United attack and create goals. All 3 of those are either not at the club or complete unknowns.