We bought Fred because he has the potential to become a great midfielder for us. However, it was obvious from the start that he needed at least a year to settle into his new surroundings. New club, new league, higher standards, new language, new culture, etc.
Is Fred a better player than Andreas Pereira and Scott McTominay? Yes. Did Solskjær pick Fred ahead of them against Liverpool? No. A lot of people seem to be interpreting this as Fred either just not being good enough, or that he lacks match fitness. It is true that he lacks match fitness, but so does Pereira and McTominay.
The reason that Fred doesn't get into the team is that Solskjær understands the importance of playing a balanced team, particularly against a team like Liverpool that will punish every single mistake we make. Every solid team consists of some players that has the mindset, form, experience and abilities to control a game, lets call these players the pilars of the team. If you don't have enough pilars, the team will collapse. While our defense seems to find their form and starting to show their potential, neither of them are solid enough to focus on anyone else than themselves at the moment, i.e. we have no solid pilars at the back.
Before the game even started, we lost a pilar in Matic. Fred is not good enough defensively to replace him in this kind of game, while McTominay is a more defensively solid player. He is a local lad that understands the rivalry against Liverpool, and he has performed well against them previously. McTominay was the obvious choice to replace Matic. We also missed Lingard before the game, a pilar from our front trio. When Herrera was injured, we lost another pilar. With these three pilars out, the team was simply starting to become too shaky. Andreas Pereira has been attached to the club longer than Fred, he is probably easier to instruct since he speaks english, and he understands the rivalry to Liverpool. At this extremely vulnerable situation, Solskjær had to go with the safe choice of Pereira ahead of Fred.
To put it short, Fred is still adapting to his new surroundings, which means that he is an uncertain card for us. He may perform in some games, but be completely useless in others. Our team is simply not solid enough to risk playing him ahead of a solid player like Herrera. Dalot has the same problem. Is Young a better player than him? Probably not. Still, Young has to play to provide experience in our starting 11 and keep the balance in our team. Solskjær understands this, this is why he is the manager, while we are putting angry posts on a forum.