The Wilderness towing is primarily improved by the addition of the CVT oil cooler and engine oil cooler. I'm sure the lower gearing helps, but the cooler is the most important part.
The thought that the Forester Wilderness using the Ascent's transmission and differential is a misconception. It does not. They never officially said what it uses, but I'm pretty sure it uses the transmission from the Outback 2.5i (still TR 580, just different range) and the differential from the Outback XT. I figured this out by comparing the numbers of the Forester wilderness with the Outback as shown in the following chart. I highlighted the matches..
|Forester||Forester Wilderness||Outback 2.5i||Outback XT||Outback Wilderness|
|Final Drive Ratio||3.700||4.111||3.900||4.111||4.444|
Also the 7 gear vs 8 gear really doesn't mean anything. Those are just pre-programmed ratios to the CVT. What maters is the overall range. When you combine the starting transmission ratio and the final drive ratio, the Wilderness has an overall starting ratio 25% lower than the standard forester.
Though the Forester Wilderness only has 0.5" more ground clearance, the height was increased 0.8" just like the Outback. After searching around for a long time I asked Driving Sports TV on twitter to ask subaru what was going on when they drove it. Turns out it was caused by a limitation of the production line and the body was lifted independently of the drive train. So it is a 0.8" lift, but it didn't get that much additional clearance. Here's a link to the twitter convo. You need to click on it to see all of the conversation.