1. Hasn't the Borders line actually largely met it's long-term projections, it just got to the 5-year mark a bit early.
2. How has the Borders line created journeys where you can avoid London?
The potential for EWR to intercept cross-London traffic is fairly minimal, it will be edge cases only of people determined to avoid London or who enjoy spending more time than necessary on the trains. What EWR will do is create an important commuter corridor linking Oxford, MK and Cambridge (and Bedford, to a lesser extent) to a wider area rather than being concentrated on the London radial infrastructure. This will hopefully allow more development to take place between those towns at places like Bicester, Winsford, Stewartby, St Neots, Cambourne etc that will provide some measure of relief to the UK's shattered housing market as well as possibly build a limited amount of economic counterweight to London and so temper the economic domination of the capital.