Yamal has played like 50 games at the age Messi made his first team debut. So I think it's fair to say he accomplished more up to this day.
Ofc that doesn't mean he has the same talent as Messi and even less that he'll have nearly as good career. Especially Messi's longevity at the top level will be almost impossible to match for any player. Even if you have the talent and abilities staying relatively injury free will become harder for players with increasing demands of modern day football (focused more on generating money rather than players's well being).
And I'm not only talking about physical effect on the players but also mental one. As
@FCBarca mentioned no player had so much pressure on his shoulders at his age. When Messi made his breakthrough we had R10, Eto'o, Xavi, Iniesta, Puyol,... and then later Ney and Suarez. So he developed in a better environment surrounded not only by elite players but also strong personalities. Almost every player in that Pep team was captain material. That leadership is something we've lacked for years now. And while he was the best player and decided a lot of games on his own Messi didn't need to carry the whole team as much until his late twenties/early thirties when his beloved amigos started to decline.
Compare that to Yamal who at 17 is playing alongside grandpa Robbie and bunch of other kids (though compared to him someone like Pedri already looks like a veteran). Our only elite player in his prime years right now is Raphinha. And potentially Olmo (though I don't rate him that high) and Araujo (if he won't leave) but they are both injury prone. But as much as I like Raphinha I think it's fair to say he's not on the same level as above mentioned players.
How long can he continue to do that before he'll break down? Hopefully won't need to find answer to that question and we'll build a strong team around Lamine. It's insane and unhealthy for any club and more so for a club of Barca's importance to be so dependent on teenagers like we've been over past 4-5 years. Yes, they are/were good and mentally strong enough but OTOH injuries affected most of them.
Hopefully Yamal and Pau won't go down the same road as Ansu (well, especially him), Pedri, Balde and Gavi. But that's the risk we were taking pushing these youngsters into the water and if we want to become a "normal" club again this needs to change. I'm not saying La Masia kids should not be given a chance but that should only happen when they are ready, both physically and mentally. They should be given as much time as they need to develop and when they get to the first team they should have someone to lean on not be the ones carrying most load.
It's also a dangerous game with expectations some kids (won't even talk about fans who think players will never make it here if they are not starters at 18, lol) will have regarding their future in first team seeing Yamal and Cubarsi. They should be more exception than the rule. It's probably too late for current generation of 16-17 yo kids at the club but hopefully in 4-5 years players of that age won't expect or even demand first team minutes just looking at their peer(s) being star(s) of the team.
So it's good we also have examples of Fermin last year and Casado this season to balance things out a bit and show you can also make a breakthrough in your early twenties as long as you are patient and hard working.