Messi’s game was not on another level. He had great dribbling and ball retention. He made poor decisions, didn’t finish his chances, and couldn’t physically impose his game on a consistent basis at that age. Mbappé was the main focus of a Juventus team that hadn’t conceded in over a thousand minutes in the CL at 18 years old and still managed to score, after taking out Dortmund and City. It’s just a different (read superior) impact at that age. Barcelona was one of the best two teams in Spain, and he had plenty of great players to help his transition and put him in winning conditions (although they still weren’t the Juggernaut Barca). I’m not a stat guru but I’m sure, to compensate for Messi’s inability to stay healthy, you’d still see his goal+assist/90m vastly inferior to Mbappé at that time. It’s okay, Zidane is my favorite player and he, arguably, didn’t even become a great player until his mid-20’s.
No. I think people ignore a fact:
Messi at 18 missed something missed the last 3 months of the season 05/06 with injury. Before that he was the best player on the pitch not named Ronaldinho vs Madrid at the Bernebeau, was the best player vs one of the greatest Premier league sides at Stamford Bridge And was putting in some world class performances week in week out both in la liga and the UCL.
Messi at 19, missed another 3 months of the season 06/07 with a broken metatarsal. This time mid-season. After he returned, he obviously took time to regain match fitness but once he did, he produced a MOTM vs Real madrid away even not taking into consideration the hat trick, scored the finest goal I've ever seen vs Getafe and produced some amazing performances week in, week out.
Messi at 20, missed 2 months of the season in season 07/08 via 2 separate injuries. Once he was back, he easily outshone Ronaldo, the ballondo'r winner that year, at both the Nou camp and old Trafford despite just having returned from injury. Again, when fully fit, no one was better.
These injuries are often ignored when comparing Messi to other players at the same age. It is also worth considering that long term injuries also affect match fitness meaning that a number of games are required for the player to regain pre injury sharpness.