Was Maradona as good a goalscorer as Messi? Well. Maradona played for Napoli in the Serie A of the 80s. Platini's and Laudrup's Juventus with Scirea (some say he was better than Beckenbauer) and Gentile (whose manmarking of Maradona and Zico in 1982 helped Italy win the WC) at the back. Sacchi's Milan. Sampdoria with Vierchowod at the back and Mancini upfront (Sampdoria won their one and only Scudetto in that era). Roma led by Falcao (you know, one of the Brazil 1982 legends) etc. So yes. Maradona didn't score 10 hattricks in a season under these circumstances playing for little Napoli. But I'm sure if he played in a stacked team with basically 10 World Cup winners on his side in an unbalanced league (Barcelona's estimated squad value: € 650 million; Zaragoza's estimated squad value: € 40 million), he would have score much more. But that's the downside of football and statistics. Statistically Mario Gomez is a better forward than Maradona.
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I don't think there is any debate (IMO) that Maradona would have scored far more goals if he had played in a team as offensive as Barcelona, for sure he would have baged hat-tricks and pokers and what not, but there is this huge difference between Messi and Maradona that no argument can can change about and that is the consistency of performing. While Maradona at his best could perform at the same level that Messi does at his best, Maradona never managed to line his best efforts over more than a few games at a time. This is where Messi really outshine Maradona as he is performing with an almost superhuman consistency.
In the case of Maradona, both at Camp Nou and San Paolo I witnessed him in games where he simply didn't show up. We are not talking about bad games here as Messi also has really bad days at the job, something all players do. No, we are talking about games where the team could have played without him and you would not have noticed there was one man less on the pitch. He simply was AWOL, a shadow running around on the pitch. Maradonas consistency decreased over the years being more obvious post 1986 WC but really was already showing a decline in his second year at Camp Nou. Some people have blamed this on his extra sportive life, with long party nights and an ever increasing drug abuse. But i think that his character is the main thing to blame here, he never really was a true professional in the sens of taking care of him self and his training.
The botton line is that Maradona no matter what team or league he would he played in, he would never have been able to match the numbers of Messi for the simple reason that he just wan't able to perform at the same level of consistency that Messi is. If Messi in a 50 match season has 5 really bad days at the job, Maradona had 15. And on the other end, if Messi in a 50 match season has 30 outstanding matches, Maradona had between 15 and 20. The difference is pretty huge when taking this into context of a whole career.