Fergie's biggest mistake...they only won two more league titles and another Champions League final. They lost to one of the greatest teams in history in the Champions League final. The leagues they lost were on goal difference with the last kick of the game and by one point to Chelsea where Drogba scored a clear offside goal at Old Trafford. Some mistake.
The revisionism of 2009-13 as the 'start of the decline' when United were very successful annoys me. United won the league by April 22nd in his last year. Some key players of the squad were ageing but if you look at the team that season - De Gea was 23, Rafael was 23, Jones was 21, Evans was 25, Smalling was 24, Welbeck was 23, Hernandez was 25, Kagawa was 24, Cleverley was 24. You can say now 'oh most of those players were never good enough'...but they were good enough to be in a squad winning leagues at the time. It's Fergie's fault for picking Moyes perhaps, but it's not Fergie's fault that successive managers made a balls of the squad.
1) Ronaldo. Fergie has reputation as ruthless manager. Allowing best player in the world who is under long term contract to leave in his best years just because "Real is his dream" was bad decision.
2) Tevez. Not doing everything and on time to keep Tevez was mistake.
3) Not signing quality in midfield where Hargreaves was injury plagued and right back where we only had Brown was mistake.
4) Selling Pique season earlier was mistake
5) Even if he couldn't stop Tevez and Ronaldo transfers then he should have bought another top players on that positions. Not bloody Valencia and Owen.
Teams have peaks and troughs, it would have been very hard, almost impossible, to replace Ronaldo. I agree on Tevez with the signing of Berbatov didn't help but from what I've read Tevez wasn't that popular in the team, fell out with Fergie and they had big trouble with his agent, was third-party ownership back then if I remember with Kia Joorabchian.
Pique was always going to Barcelona, he's a hardcore Catalan, that's just hindsight. You just said Rio and Vidic was the best defending duo in the world and Pique wanted a starting position. There's no way he could get it at that time.
Bloody Valencia was on PFA Team of the Year in his first season and won United player of the year in 2011-12. Valencia was a very good winger, then a very good full-back late in his career, despite some horrible injuries. Valencia was a fine signing. Owen was free. Agree about midfield.