Gotta ask, did you watch the Euro 2004 tournament?
Because it sounds a lot like something someone who wasn't watching his performances back then would say. He was the star of the tournament. The most exceptional teenager to play the game. As the question asked, he was already, by that time, far more accomplished than Mbappe in his career, and he was playing against bigger talents.
I watched Euro 2004. Rooney was brilliant. We have no Euros to compare for Mbappé. From the games Mbappé HAS played - we are looking the same level of talent Rooney showed as an 18 year old. Mbappé scored almost 30 goals this season, and no opposition he has faced has proven a step too far for him. I see little reason to think he'd have struggled against the Swiss or Croatian defence of 2004 either. He frightened the crap out of Juventus' defence, as he did against everyone else.