Well, I don't think anyone ever thought once that Mbappe was a bad or useless purchase, but it's simply that he had to find his place within the team, he's certainly young and is fitting in, in fact he seems to have really integrated,Now he just has to prove how many goals he can score
Well, for me I think his already fit into the team within a short period of time, yes he had a shaky start in the Spanish league but I think it was less than 3 - 4 months it took him to adapt to the team and the league in general and how his becoming a monster in front of goal for the team. Some people thought it would take him a season or two to fully adapt but it took him few months and his taken the league by storm as expected because he was already a big player.
He is a French star who has been big for a long time and is expected to have a very bright future. Mbappe has that talent, but since his move to Real Madrid, things have not been as harmonious as they are now. He has a big ego and has not yet adapted, especially under Ancelotti. Perhaps Ancelotti does not yet know how to deal with him to make him better with Real Madrid. and don't forget that Mbappe's move to Real Madrid was a free transfer, which is far more advantageous than any other option.
Today, we see that opportunity. Mbappe has become a reliable and dependable weapon, and it seems he has started to develop a very good chemistry with his teammates on the field. This is a significant step forward.