On the other hand, starting in about a year's time, large numbers of passengers travelling from Woolwich or beyond will swap from SouthEastern to Crossrail, so trains around Greenwich etc. will be less full. Also, increasing the frequency along that line requires more paths to Cannon Street, which basically don't exist. I would expect the DfT to be well aware of those issues when specifying the frequency along the Greenwich corridor.
What would be good though would be keeping the same 10-minute frequency at evenings and on Sundays.
On the contrary...
Just because the trains may not necessarily be full and standing the entire way doesn’t mean that the services won’t be both much busier between, say, Gravesend and Abbey Wood as they are used to feed the new behemoth that is Crossrail. Indeed, the provision of something akin to 4tph from Gravesend to Cannon all stops via Greenwich and 2tph from each of Barnehurst and Crayford (starting back from wherever) will be extremely important.
It does, however, make the prospect of 8 car Ops every 7-8 mins as a clockface service via Greenwich all stops vastly more attractive as people seek to connect with trains running every 5-8 mins depending on the time of day. Moreover, a lesser number of people on trains east of Charlton through to London freeing up capacity for people in the Westcombe / Greenwich / Deptford corridor makes that service indeed more attractive; and passengers who seriously need Blackheath can use the 53/54 from Woolwich or the 108 from Westcombe Park or those going to Lewisham can get the DLR.
Any notion after Crossrail opens (serving, for example, Liverpool Street / Farringdon / TCR / Bond Street / Paddington) that people seriously want to go from Erith or Belvedere to Charing Cross on a direct train is bogus. They will all want to get on the vastly quicker Crossrail to the heart of the West End or indeed to the City. Even those who want St Pancras will use it to Farringdon!
If you’re in Charlton and you want Charing Cross nobody could possibly complain that a 7-8 minute frequency of trains off-peak and peak with a simple escalator / elevator change at London Bridge onto 2-3 minutely trains to Charing Cross is a difficulty. Indeed, not being on a train that is sat at Tanners Hill either up or down waiting for a path or sat in the platform at Lewisham waiting the road over the diamond is a bonus in itself.
The simple point is this: a clockface timetable from Cannon to Greenwich, Woolwich and Sludge to continue to Dartford / Gravesend / Barnehurst / Crayford is the single best outcome without all this nonsense asking for through journeys to everywhere. In fact, if I lived in Erith I’d be standing up screaming for a 7-8 minutely service to Cannon St from 0600-2100 because I know if I need to go to Blackheath, Lewisham, Waterloo, Charing Cross, Peckham Rye, Denmark Hill, Victoria or even places like Hayes, Grove Park and New Eltham the world extends beyond a piddly half-hourly train via Blackheath that I didn’t used to have and likely won’t have in the future.