Rooney actually was not as much more proven than Højlund at the time as you make it sound. There is some hindsight bias here.
He came from Everton who were battling relegation in his last season. He scored the same number of goals as Højlund in the league - 9 (and actually it is funny that much of the thread here is people not being impressed by his goalscoring record). Rooney never played in CL. Yes, he scored 4 at Euros (all against relatively weaker teams though) and he played in PL - but he was more risk at the time as it seems now after the fact.
and while we are at it - what has Muani „proven“ much more than Højlund? He has a grand total of 2 goals in European club competitions and 1 international goal in his career, plus one good season a team who finished 7th in Bundesliga (Weghorst had 3 seasons outscoring Muani‘s last season in a similarly ranked team in Bundesliga). he would be almost the same risk as Højlund I‘d say.
Of course, goals/team league and position is far from everything. But I do not understand arguing that Højlund is much more risky than Rooney in 2004 or Muani in 2023.Riskier, yes - but is it much more risky? And saying that he „has not proved anything“ compared to them? Would not say so. And you are literally dismissing him based on simply age („child“) and appearance in your post, come on.