It’s more to do with reversing trains, than the central frequency. There is little advantage in running every train to Cockfosters, or running exactly half the trains to Rayners Lane/Uxbridge
You need to be able to empty the trains and reverse them, without delaying following train, and in an ideal world would have more 3 road stations with middle track for terminators.
As an example if crossovers were installed between South Ealing and Northfields, might be able to use both middle platforms at Northfields for reversing, with through trains able to switch to outside of islands to go round them. But don’t think this is planned.