I am sorry you felt that way. What you have stated above is not accurate and it can be easily verified by anyone on Citymapper or the Journey Planner on the Transport for London website. It takes 10 minutes walk to the tube station and 20 minutes ride to Oxford Circus (6 stops) for a total of 30 minutes to get from the flat to the shopping heart of London, Oxford Circus.
Like all big metropolis, London relies very much on the tube network; Seven Sisters is on the Victoria line, the most reliable and fast line of the entire network, the only one that guarantees a train every 100 seconds max, on top of being open 24 hours at weekends unlike other lines.
You could stay in zone 1 on an old tube line and I can guarantee you it will take the same amount of time to get from A to B.
Also, yes, all the tourist attractions are in the city centre. However, Seven Sisters is the new up and coming area of the East end and offers things that only Londoners usually experience as well as those visitors that aren’t just looking for tourist attractions but for something more original and unique.