There are several drivers who do well in lower formulae and come to f1 and then fizzle out. However, I think it's completely possible for someone to do average in lower formulae, then make it to f1 and acclimatize well and make it work out great. Hopefully this is the case for maldonado over the coming years
But this is the thing. That is not the case with Maldonado - he has a well above average record in lower formulae (2 titles including the GP2 title, wins at real racers circuits including Silverstone and Spa, 23 wins and substantially more podiums throughout his progression to F1 - average?!?), yet for some reason (well we all know the reasons - they are because he didn't start with a competitive team at the time, and because he has financial backing) he is given that tag, which under examination simply doesn't hold up and is entirely unfair!
Other than because the Williams has just become competitive for the first time in years, so take the team name out of the equation and ask yourself - based on his winning record in terms of races and titles, why should we be surprised that after a few races with a competitive car to get used to it that he's in the picture for podiums and wins? I genuinely cannot think of any reason other than unfair bias and unfairly low expectations that aren't actually based on any evidence.
I would say though, that I think Maldonado is in a good position due to this unfair perception, as he doesn't have as much pressure on him as say Hamilton, Alonso, Schumacher etc. who are
expected to win and are glorified / persecuted depending on how they do from race to race. Maldonado has the ability to perhaps 'fly under the radar' so to speak.
Favourite racing series: F1, Indycar, NASCAR, GP2, F3, Formula E, Trophee Andros, DTM, WTCC, BTCC, World Endurance... etc. etc.