You're never going to know how good a player is unless they're given a fair crack of the whip. Hannibal is the best player in the academy, if the best player in United's academy isn't "that good" then we're clearly doing something wrong.
I do agree, he should've been given games under Solskjaer and then Rangnick, and we'd likely have a much better understanding of where Hannibal is right now in his development.
Both Rashford and Matic have highlighted Hannibal as someone that has really impressed them. Matic in particular has said that Hannibal really surprised him with the quality he possessed each time he was involved in first team training, and he was looking forward to Hannibal getting more minutes in the first team. That's high praise coming from a player like Matic.
And believe it or not mate, the games he was involved with in France with Monaco, he was utilised as a playmaking #8, who got involved in the deeper build up phase, where he would routinely drop deep to collect the ball from the CBs. And in the 5 or 6 games I watched with him in the Monaco u17s, he never once lost his temper. And then when he arrived at United, he was utilised as a #10, in a position the player himself said he had never played before. But credit to him, he adapted and showed his versatility in multiple areas of the pitch.