I think the biggest problem is thinking that Mbappe is the best football player in the world. Yes, he achieved great success at a very young age, everyone thought of him as having the quality of Messi and Ronaldo. He was quite successful, but does he play well enough to save the whole team when something goes wrong with the team? People's expectation was that he would be a great star player, and when he came to this team, it was said that the biggest star in the world was coming. People do not like it when they see such a performance 
The assumption about Mbappe being the best player in the world is not wrong and it is true. It does not mean that I support it but have players like Messi and Ronaldo never failed penalty kicks in the past?On the one hand, I think Mbappe just does not have the mentality to be with one of the big teams in Europe even though he was initially very recognized at PSG, but in fact the competition there is not too strong.
So what Mbappe is experiencing right now for me is just a bad start but it will be a valuable experience. Just look at the next few seasons. We will see how Mbappe will be more recognized than now.