Don't get me wrong, I actually like the guy, he is a wonderful footballer, I even own a France shirt of his. His NT career has been AMAZING. He didn't do much in the Euros, but on the two World Cups he has played he was incredible, he has the potential to finish his career as one of the best WC players of all time, if not even the best if he's a little lucky.
But, if we only focus on his club career, has he achieved anything as great? At his age, Messi and Ronaldo had already won UCL, Ballon d'Or (Messi multiple ones), threepeating the two best leagues in the world and destroying every team in the world in general. Haaland who is his main rival according to the media and 2 years younger than him, left Norway, played in Austria, joined Dortmund, then joined Man City and finally won a treble, finishing 2nd in the Ballon d'Or. All that in a matter of 4 years.
Meanwhile, Mbappe has been playing in the exact same league for 8 years now, a league that's currently ranked 6th-5th, with potential to be even 7th. There's nothing wrong with staying in the same team, even in a less competitive league, if you actually dominate the UCL. Even PSG board members have stated that UCL has been their number one priority for years. But, the reality is very far from that target: round of 16 exits, humiliations, now they might even not get out of their group. Mbappe has been very underwhelming in the UCL this season, with 3 goals, 2 of them penalties. The only time PSG came actually close to winning the competition was 2020, but Neymar was their main man, Mbappe hadn't scored a single goal past the group stages. So, his best UCL season so far remains... 2016/17 for Monaco, since then it has been underwhelming for him, or his team, or both.
One might say that UCL isn't the only competition out there, surely. Mbappe has been Ligue 1's top scorer for 6 consecutive seasons and has won the competition 6 times. It's very impressive. Or, is it? Mbappe scored 29 league goals last season, while 32 year old Lacazette scored 27, playing for 7th placed Lyon. In comparison, Lacazette had scored 5 goals in 30 EPL games in the previous season (2021/22) and had never even scored 15 league goals in EPL in a single season. Many people memed him and called him "Alexander Lack-of-threat". But surely, he might have found his good old self now, it has nothing to do with Ligue 1. Let's see other players who scored more than 20 goals in the competition last season: David, Openda, Balogun, Habib Diallo. Very decent players, especially Openda, but not exactly what one would call "world class". Compare that to Messi and Ronaldo competing with each other and Suarez, Villa, Eto'O, Griezmann etc for the golden boot, or Haaland competing against the likes of Kane, Salah, Son etc and you can see the difference. In 2021/22 Mbappe competed with Ben Yedder, Terrier and Moussa Dembele. Other players that scored 20 or similar amount of goals in that league include Nicolas Pepe, Mariano Diaz and Balottelli. The definition of meme players. So, Mbappe's numbers in Ligue 1 barely matter, the competition is bad and most players who score tons of goals there fail miserably in other leagues.
So, if we only look at his club career, so far it's just a guy scoring a lot of league goals outside of the top leagues and nothing more than that.