Still maintain he was a decent signing.
That is one of the core elements of his story I think. When he came, he was one of the best players in the squad, reputation wise. He also came at a time, when our midfield needed serious improvement and the squad in general was pretty flat. The issue though was, I think, this transfer was carried by the supposedly "great return story". And I think, it carried club and player away. We obviously hadn't understood what the conditions where, to make him thrive. And that being said, this definitely applies for big chunks of the fanbase back then and reading the comments here, even today. Tinkering with his position was a factor. His team mates were a factor. Him being looked at as a player to lead the team was a factor. And there were probably even more variables in the equasion. All in all, it led to many disappointment all over the place. Raiola and some of Pogs public statements piled onto it even more.
Who knows what could have been. I am pretty sure, he wouldn't have become a world star at Madrid for some of the same reasons as with United. But another team, with a better running "machine" ready to optimize the conditions for Pogba to shine, I think, he could have become a bigger name than he is now.
That being said, I think, he arrived at the scene 10 years to late. Would have been a bigger star in the 90ties and early 2000s. For me he is one of the chapters of what is wrong with Uniteds recruitment, headline "Go for players for the wrong reasons"