Only a complete fool thinks he was better in 2012. Messi was still young and learning, over the years he's gradually learnt he doesn't need to go from 0-60 when he's in possession, plus he had Iniesta and Xavi in their peak years behind him, he could stay forwards and deal the necessary damage.
Nowadays he's all over the midfield and attack, and he's learnt he doesn't need to beat 3 men to create a chance, he can do it with one pass. Goals may not be as frequent as they were back then, but that's largely down to a big decline in the team around him IMO.
Messi in the 2014/15 season stomps all over Messi between 2008-2013. From January onwards once Enrique accepted Messi can do his own thing, Messi (near single handedly at times) won the treble for the Club, and that was by having a far bigger influence over the attack and midfield than he ever did in his earlier years.