If you go the Disco route for serious offroading you will need much more barwork and protection than the Defender, whose bodywork is neater, boxier, narrower, and as far as I can see without referring to the manuals, has better departure and approach angles. So less panel damage with the deefer.
Having said that, there seem to be times (eg loose steep long inclines, large step-ups etc) when a Disco with a V8 and an auto box does have an advantage.

