All the damage was done in the 2009 summer transfer window and onwards.
2009: Valencia, Obertan, Diouf, Owen. Super underwhelming considering what we lost.
2010: Bebe, Smalling, Chicarito, Lindegaard. Potential and long-shots.
2011: De Gea, Jones, Young. Replacement keeper, potential and solid PL winger.
That three-span window was really critical. As we lost Ronaldo and Tevez, while Ferdinand, Vidic, Scholes, Giggs, etc. were all nearing their expiry date, we didn't bring in a single established high-profile player. The 12/13 season papered over cracks with a short-term solution in van Persie, but we've been playing catch-up ever since. Fecking Glazers.