He's not a true ETH type striker and thus has to play on Rashfords position. And yes of course Mbappe is clear of Rashford, but you would be replacing our best player, not the players that need replacing. I'd rather go for Kane, Vlahovic or Osimhen who are IMO also safe bets but less diva tendencies and better tactical fits for the position we need strengthening the most. Even at France Mbappe plays on the wing with Giroud/Benzema at the 9.
I also have doubts about his demands and no I highly doubt Rashford will get a Cristiano like contract since United changed their wage structure. They don't want to hand out these massive contracts anymore which is a wise decision.
Mbappe is great, maybe even the best in the world right now, but is it so ridiculous to have doubts about that move? It's exactly these box office transfers that set us back so bad in the past. Pogba was supposed to be the best CM in the world but couldn't be arsed to do any defensive work. Di Maria was one of the best players in the world when we bought him and did feck all.
If ETH would greenlight it I would be on board, but as long as he doesn't I'm having doubts. Mbappe is a player you add when you have your entire team set up, we still need loads. A CM, one of the ST's mentioned above, a GK and another CDM in case something happens to Casemiro. Even a CB to replace Maguire.