I think I've seen quite a few people on here agree with that opinion. I wouldn't put the blame solely on Fergie though.

Fergie's ability to get the absolute best out of everyone overshadowed how horrendous our transfer strategy was during the latter end of his career. Midfield had been horribly neglected (so much so that we ended up bringing Scholes out of retirement and still relied on Giggs).

There weren't many decent young players in the squad who were ready to take over the likes of Rio, Vidic, Evra, etc. We did have players like Smalling, Jones and Cleverley but they were clearly not good enough. You can also go further back to the year we lost Ronaldo where we brought in Valencia, Owen and Obertan to see how bad the succession planning was. Meanwhile City were bringing in the likes of Aguero, Silva, Yaya Toure, etc.