The direct trains to Charing Cross ran every half an hour apart from rush hours in working days. The last direct train was 23.12 (maybe slightly later!) from Charing Cross, a bit early, but it was unchanged for twenty years or more as was much of the timetable for a long time, and there was a 2345 from London Bridge. After that it was a train to Lower Sydenham and a long walk. I'd sometimes get the much later train from Victoria and walk from Penge East.

There was no Crystal Palace loop to Victoria certainly in the early 90s and at one point we went from four to three trains an hour to London Bridge, but that was quickly reversed and then when rebranded the South London Metro the Crystal Palace/Victoria loop was reopened, initially with limited service but swiftly to the two hourly service we have today. But it doesn't half trundle and shockingly long train times to Clapham Junction and Victoria. Annoyingly the Crystal Palace to Victoria section to Clapham Junction is not part of the Overground, which is treated as a tube fair, so if you change at Clapham to get onto another train service it is an additional journey on Oyster.

I found the direct train to Caterham, that meshed with the Tatenham Corner, great for a walk or cycle, again now gone, as were the trains to West Croydon (replaced by Overground) but often went to Sutton which was useful, say for kids going to Wilsons.

But hey ho, I am an extensive user of the Overground to Canada Water, and now of course to Whitechapel to use the fast Lizzy Line. Whitechapel as with Bermondsey, takes you near to central London (or say Brick Lane and Shoreditch) without going into Zone 1 (that was part of the deal for the Overground in that it goes into Zone 1 when it shouldn't really but to bring in extra revenue say for those going to Highbury and Islington). For nerds and tightasses (which I may or may not be) you can go the long way round for some journeys via Stratford to avoid Zone 1.

Nothing to do with this thread but when you go to many international airports you get cheap fast transit into the city. But in London we have expensive options, the Heathrow/Gatwick/Stansted Express and the last one isn't an express. Fortunately the Lizzy line will put the first out of business, there are plenty of alternatives for slightly slower trains to Gatwick and if you time it right it is cheaper and quicker to get the coach from Stansted and pick up the tube at Stratford to get home (wont put the lines out of business as many foreign travelers are not aware of cheaper alternatives and some on business wont care)