I live in Zone 3 and completely agree with @AlbertBealeI disagree. I live in Zone 2/3 (I’m sure you can guess where based on my username!), and the integration of bus and tube fares would switch me from the car to public transport for many journeys.
For example, if I want to go to Westfield currently via public transport, it would cost me £1.55 on the bus, and then £1.50 on the tube. That’s each way.
£6 per person return - might as well drive and park, especially if I’m travelling with someone else.
Tube and train good for radial journeys and I use them.
Orbital journey useless and better tube /bus fare integration won't change that, buses currently OK for a small number of orbital journeys (the number of changes quickly escalates (typically 1 change every 1.5- 2km) but it is mostly heads towards car for longer orbitals.