Defence is not THE key for any club at any level in any league. This conclusion is dictated by the logic of 3 points for a win, but only 1 point for a draw. That logic emphasises the importance of attack over defence.
The notion of 'building from the back' is just a tired old cliche, dating back to the era when a win gained only 2 points. In the modern era the midfield is the key area to build from, especially the ability of the midfield to support strikers and unlock defences for strikers.
Seriously,
A spurs fan comes on a Villa site quoting LOGIC