In part, the problem for Messi is that he formed himself as a player playing in the greatest football team ever, with 2 of the best midfielders of all time, and one of the best right backs of all time. So he was kind of used to move less, conserve energy, knowing that the ball would get to him in the right spot, with the right pace, just the way he wanted it and the way the Barca style demanded to happen. Playing with prime Xavi, Alves and Iniesta makes your job so much easier you wouldn't believe. Now he is a position where the service he gets is of way lower quality, the difference is like night and day. Passes being made towards him are struck too hard, either short, either too late, or with the wrong angle, all sorts of passing problems, that he just didn't have at Barcelona. This delay is critical because it allows the opponent to prepare and block him better.
The fact that Messi carried Barca back in the day is the most idiotic idea I've ever heard. He had a lot support. Like really a lot. Now that's gone, and he declined physically (that's clear, he's way slower and less explosive than at his best) it's unsurprising that his performances aren't the same against the big teams. His fans say he's more of a playmaker now, picking passes of genius left and right, but that mostly happens against weaker sides that aren't defensively disciplined. Top sides and hard working teams who put in big defensive displays aren't that impressed by playmaker Messi. They can isolate him and crowd him and force him to play safety passes.
He can get around those issues and continue to be decisive, but in the absence of great service, you basically need to compensate that by being more motivated, working harder off the ball. In short, making himself available more, rather than just assuming that the other players will do their job and will find him with clever passes. Again, he ain't playing with Xavi, Iniesta, Alves, Villa, peak Busquets, Eto'o, Ronaldinho, Henry etc. Solution is to stick to a more advanced position, put in more intense effort and don't try to cover a lot of ground.
I'd move him back on the right, not hugging the line, but playing as a forward coming from the right side in on his left. This Messi that drops deep and acts like a no10 midfielder, a la Pirlo, ain't impressing me.
