Double amount of games doesn't mean all that much at this point in their careers. He's played one season in the Brazilian second tier and another season worth of matches at Lille, wasted a year in Croatia in between too for good measure.
I don't buy this idea of struggling with "how to cope with pressure". If anything that'd be the first thing that shows when you switch countries and leagues, on the contrary how do you go from MOTM awards to looking like shit after a while? I'd say his level dropped because a) fatigue and b) whatever coaching and training with team mates he was receiving at Arsenal clearly did more damage than it helped. You wondered about the same thing recently regarding Martinelli, training is by far the most important factor with any player looking good or not on match days.