Interesting review. Looking at it slightly differently from an owner/real world buyer perspective...
With these two vehicles it's silly to not mention reliability and durability. Maybe some folks don't care, but GX buyers generally do and the Defender's reliability record has been positively abysmal so far.
Motor Trend seems to have a brief memory. I belong to a few different GX groups and there are many Land Rover folks who are ready to make the jump to the GX after significant failures/repairs with Defenders.
It seems like a key deciding factor in Motor Trend's final scoring was on-road manners. I understand that and it's a fine point, but in this class there are many folks who prefer driving BOF SUVs to unibody CUVs. I'm one of them. If you're going to build and offroad one of these for years to come, rough impacts on an aluminum unibody with air suspension vs. a body-on-frame steel chassis with conventional steel springs is going to be a difference you feel (your bank account agrees).
Land Rover's inclusion of an air suspension on the Defender to help with ground clearance and approach/departure angles was a good one, especially since it's unibody. No denying bags give it an advantage over the conventional GX suspension, but unfortunately air suspension failures and problems are one of the most common Defender issues. Also it seems like any of the Defender's offroad shortcomings were chalked up to the tires, but the Goodyear Wrangler All-Terrain Adventure is a tire Land Rover specifically spec'ed for the Defender so..... not sure what to say there.
Another matter of personal preference, but I think the Defender interior is pretty awful -- especially for the price. It looks like an update of the 2011 Honda Element interior to me, and certain elements like exposed screw heads and rubber flooring seem really out of place at $90k. While I don't
love the 3GX interior, I prefer it 11 days out of 10 to the Defender's.
What suspension work isn't cheap - a lift kit on a GX or air suspension repairs on a Defender?
Edited for clarity: The GX 550 was easier to drive off road and was more capable despite having less ground clearance, but the Defender was almost as good offroad and drove better on pavement due to being a unibody CUV with air suspension.
At the end of the day, it's cool to have these two great options but there are plenty of people who wouldn't touch a Defender with a 10 foot pole due solely to reliability. Oh well. Choose wisely!