My experience of using the Central line is that it is quite normal for branch intervals to be very lopsided that side of London, in favour of both branches (or none, dependent on your view).
I have no idea why or how exactly this happens, but it isn't exactly right for TfL to claim a good service is operating on the Central line when it does.
As I understand it the Epping trains are commonly from West Ruislip, and the Hainault trains are commonly from Ealing, they are like two separate services interleaved. This has certain advantages in the core, where a disruption of any of the branches still enables at least a 50% service, normally adequate outside the peaks, but it is disingenuous to claim Good Service, which as I understand it is based just on central London intervals/wait times, when certain destinations are disorganised. It's really an issue of reducing the status of this entire substantial and lengthy line to two words.
Regarding all the "anyone outside the GLA boundary isn't allowed to comment on Underground services", etc, attitudes, in actual fact a substantial proportion of the Mayor/GLA money is provided by central government from national funds, in just the same way as other local authorities, though of course in different proportions. Even Wikipedia summarises it as "The Greater London Authority is mostly funded by direct government grant". There are obviously revenue streams from Underground fares, etc, but a key issue is that this overall government money does not identify just what it covers. A past discussion, long ago, was that a relevant amount of it was to cover the various (not just Underground) operations outside the boundary. The Met Police, for example, have a substantial national remit. Thinking that only those areas where voting for the Mayor takes place are entitled to be considered is just wrong - among other things a very substantial proportion of even Zone 1 passengers actually live outside London, but are using a national transport resource in their capital.
Incidentally, when long ago I used to use the service regularly to Wanstead (past posts refer), if disorganised in the core to an extent of not being able to get into the next train, I would get the first possible and change if needed at Leyton (not Leytonstone, with too many others trying a similar tactic), the trains having typically shed numbers at Liverpool Street and Stratford, and that always worked.