Yes! Densely populated parts of inner London that are also major passenger interchange points ideally would be served by several lines; and by various bus routes as well. Hackney is without a tube service only because various Governments have delayed giving the Hackney/Chelsea lines the go-ahead.

The number of passengers using Stratford is extremely high compared to any non-passenger interchange station and to several that are interchange stations. Providing an extra route from Stratford to Docklands is most certainly not the only thing the Jubilee Line achieves.

All places in London are only a bus ride - or three - away from a railway station, but when the Piccadilly Line was extended to Cockfosters there were far fewer bus services in the outer suburbs than now and a far greater percentage of London's population worked in central London. In addition the manually operated semaphore signalling system did not allow close headway between trains. The idea that thin-on-the-ground 1930s bus services would transport the working populations of Cockfosters, Oakwood and Southgate etc. to various railway stations where they could cram into steam trains that were already overcrowded is unrealistic. I'm not at all surprised that the Piccadilly Line and Northern Line were extended northwards. Today's situation is quite different of course, politically, financially, socially and technically, and decisions made several decades ago have minimal relevance to today's problems.

Your last paragraph makes no sense at all in this context.