I don't get the Napoli were average line. The two seasons before he joined they finished 9th and 11th. His 1st season they were 10th. The 1st title they won it was their defence that won it for them. Juventus scored more goals than Napoli, but Napoli had a much better defence. Can't imagine Maradonna did much to help the defence. Maybe signing Italian internationals like Ciro Ferrera and Salvatore Bagni did though. Add in that they had the likes of Alameao, Careca and di Napoli in their attack and it was hardly the rubbish side they made out to be.
When they next won the league, both Baggio and van Basten scored more goals than Maradonna. His record in Europe is also poor, with Napoli never really impressing, despite the absence of English teams post Heysel and it was Milan that dominated Europe around that time. In 25 European games for Napoli he scored just 5 goals. Messi in contrast has 49 in 65 European games, with a stunning 12 in 7 this season!
Messi also has a comparable goals per game ratio at international level, despite never hitting his Barca form for Argentina. A lot of all this seems to reflect the
reminiscence bump, which suggests that whoever is at their peak during our adolescence is thereafter regarded as the best ever. That and of course that during that time Maradonna hit his peak against England so he's at the forefront of our national consciousness.