RvP had as many 15 goal seasons in his first 6 years at Arsenal as Hojlund did in his first year at United, for what it's worth. At Hojlund's age he had 42 goals in 157 games.
At Hojlund's age Alan Shearer had 43 goals in 158 games at club level. Hojlund has 51 in 169. Gyokeres had 32 in 95 games (almost all of them in the Swedish league). Harry Kane had 21 goals in 91 games. Ollie Watkins had 47 goals in 151 in the lower leagues
I think people, really, really don't understand how hard it is to be a Premier League striker and how late most of them develop. None of that is to say Hojlund is guaranteed to end up being a really good player, but having long stretches without a goal, inconsistent busts of form and being heavily reliant on confidence is exactly what you expect from a striker who has just turned 22. I don't know if selling him is the right choice, it would depend on who was available to replace him, but if the suggestion is to just buy another prospect and see how they do then we'll be stuck in a never ending cycle because we're nowhere near the point where we can write of Hojlund yet.