Mourinho was wrong the moment he joined the club. And it was Woodward's biggest mistake in his tenure to allow Mourinho to operate independently from the club's newly formed recruitment structure. Where around 50 full-time scouts were brought into the club in 2016, and the guys at the transfer ground guru said it was one of the most impressive line-up of scouts they had come across. Just to give one example, the scout from Genk in Belgium was brought in and he's the scout who is credited with discovering the likes of De Bruyne and Courtois. But if your manager refuses to work with the club's newly formed recruitment structure and decides he wants to work with his own independent scouts and is allowed to do so, then the car crash is just around the corner. So we repeated Liverpool's mistakes where they agreed to Rodgers' conditions of not wanting to work with Michael Edwards and the people running recruitment and hence Liverpool were forced into creating a transfer committee with two parties (manager v club structure) constantly being in disagreement.
And as the telegraph journo Jason Burt put it, every signing made during Mourinho's tenure was his own signing supported by his own independent scouts. And that was allowed to happen by Woodward, even after the recruitment revamp was close to completion which was completed in 2016. That is as dumb as it gets because in that situation you can't best utilise the scouting network or develop the football structure to a high level. Mourinho only cared about himself and his CV/resume and didn't care about developing the club's newly formed football structure and hence we gave rival clubs a massive advantage due to those clubs appointing high calibre head coaches who were comfortable working under a group of people who supported the head coach with data science , scouting, sports science etc to improve performance at all levels, which would help the head coach.
So it's nothing to do with signing Pogba but rather not knowing how to develop a football structure due to signing managers like Mourinho and not signing head coaches like Klopp. Because Klopp understood that his success is linked to the development of Liverpool's football structure and hence he went to Liverpool and worked with the club's football structure and not without them.