Let's be honest, Messi started slacking even when Pep was here. After this much time of carrying team on his shoulders it gets hard to be your own disciplinarian. And once the power shifts from manager to player all kind of other problems arise.
In short, the blame for current state of things lies on both the board AND players.
Pep's followers should remind themselves of his latest statements where he said he left because he couldn't motivate the players anymore. Do you need a translation?
Cant wait to take a dig at Pep can you? Still butthurt that he left?
"I cant motivate the players?" could easily mean that he wanted to sell some players like Cesc, Alves etc. as rumoured and wasnt allowed to. And what has transpired since he left with the idiotic board letting deadwood fester in our squad and not reinforcing with Puyol as the new signing every year, im inclined to believe those rumours. Look what he's doing at Bayern, reinforcing the squad to the point where he almost has 2 world class squads in one team.
Regarding Messi, yeah he may have allowed Messi leeway to get the best out of him, but you cant go around assuming that Pep would'nt have clamped down on him seeing his current (lack of) workrate.
Regarding power shifts from manager to player, yeah both board and players are at fault, but its the boards primary responsibility to prevent it from happening. In general players especially veterans like Xavi have big egos. It has always happened over time that sometimes the egos get too big for the club (Ronaldinho etc). and its the boards responsibility to back the manager which hasnt happened.