Also look at the less glamorous fleets, transports, MPAs, ISR, trainers and others. You have a dozen of these half a dozen of those etc. Often unique airframes or multiple marks and a range of ages and configurations of outwardly similar airframes. This is managed and supported.
For the air combat force you would still concentrate the different marks and configurations within specific wings and squadrons limiting the adverse effect on frontline support. You would never want a F/A-18A flying in the same Sqn as Fs but in the same airforce, different units, no problem.
Anyway, I will pull my head in now and stop derailing the thread. Its just that picture you posted brought back to me the costs associated with HUG and CBR and that if we had batched our buys and planned for a mid 2000s replacement batch there would not have been the need for the upgrade. The C and D s already had the new systems and beefed up structures and an E/F buy would have filled the rest of the gap, leaving us ready now, stress free to introduce the F-35 to service.