Muller it's ten times more intelligent than Mbappe, he is a great player with a carreer that more talented players should had and wished had.
Yet to make an example with another player in his prime: Diego Milito in 2010, there is a reason why he would never sit beside Messi, nor live any remotely the type of pressure Lionel had to endure even till today and why also sadly he was very unfair treated when he didn't even got into the 30 best players that year for the Ballon D Or (the real big miss of that award that year). Milito even in his best year, winning everything, being excellent and clutch he operated in very a different scale of expectations.
I'll give just little sample of what I mean.
No one remembers that miss from Andrés and he had quite a number of others similar misses (we all are going to remember his goal versus Chelsea and Holland), as had Xavi and even Lucho that lived for goals. Some Juve fan will remember Buffon's saved, but the title after the match if Barca is defetead and Messi doesn't score is: Messi did nothing, even if just that assist is beyond excellent.
On the other hand, of course sometimes when Barca wins, everything was about Messi, that isn't true either, but it's an entirely diff world some players live in. And mostly it's because of the atributes and type of player some players belong, that is quite different of those with the atributes of a Muller, a Diego Milito or even trully special lads Iniesta.
PD: I'm not saying that Mbappe it's a talented as Messi, or Pele, or anything like that, but he is the type of player whose atributes would put him in the Upper echelon and people would lay their eyes on them with a microscope, for the good and for the bad, it's a world of hyperboles.