I absolutely agree that it is not good enough. The attitude appears t be that you have London Overground and be grateful, little people of SE London for 2 trains/hr. I participated, with others, on a call with Ellie Reeves where she voiced her displeasure. I did also write to Department of Transport and they said, not really up to us. Unfortunately, I don't see quick changes as:
1) Southern are not greatly interested in running a local chuff-chuff from London Bridge to London Victoria. They would probably argue they have to maximise income and reduce costs in the post pandemic world. So I would wager they are more interested in their longer, more lucrative routes.
2) London Bridge to London Victoria could perhaps sit in London Overground/TfL, but
3) Tfl does not have the money to take on lines from Southern
4) Without getting too heavily into politics there are contentious debates as to the funding of TfL which are unresolved.
5) Possibility of strikes, further reduction of money for the rail companies
Of course the longer there are no LB t LV trains, the less demand....because no trains to carry them. Which I suspect is Southern's game plan.
The only slight positive I see is that the advent of the Elizabeth Line should take some traffic from the Canada Water interchange (though you still have to use the Overground of course!). I tried Overground to Whitechapel and Elizabeth to Paddington - about the same time as into London Bridge and the tube, but much easier (if you avoid the rush hour!). The same route gets you to Farringdon and Tottenham Court Rd - the stations are so large they serve the footprint of 2 tube stations (e.g. Elizabeth Farringdon station covers both Farringdon and Barbican.