Can't remember if this has been answered already - but, while I understand some of the TL services have to go "somewhere", why did they not just do a straight swap and keep the TL service with the old 'semi-fast' calling pattern via Lewisham/Blackheath/Woolwich? Not a local, but from an outsider's perspective, the 'old' service seemed to serve a purpose, of linking Medway and the larger stations/interchange points along this line, quite well. A bit like an eastern version of the Reading-Staines-Waterloo. What we now have is the equivalent of a Reading-Waterloo all stations, stopping at St Margarets, Wandsworth Town, Queenstown Road and all the rest!
I think it was timetabling issues and constraints were the cited reasons I recall, as to why this became a stopper, the timetable was also padded out, so even though the Rainham service skips Erith, Belvedere and Woolwich Dockyard, it is still slower than the CX-Dartford service which calls at those stations but not at New X & St. John’s obviously and the Cannon Street rounders which does call at every station.
Yes the old Gillingham service was indeed like the Windsor & Reading services from Waterloo, I would say this it had more in common with the Windsor service, which calls at more Greater London stations (Vauxhall, Clapham J, Putney, Richmond, Twickenham, Whitton,
Feltham, Ashford Surrey, Staines then all stops to Windsor) as opposed to the Reading service calling only at Clapham J, Richmond, Twickenham, Feltham & Staines.