I will explain a little later on why I made that statement. I agree the Sorento is doing well in the circumstance you are describing but any AWD cars would be just as good. The way you tested the "4 wheel lock" (because this way to describe the system is very misleading and inaccurate, -not your fault but Hyundai/Kia Marketing's) is not indicative of its short comings.
sooo, they're lying?
https://www.youtube.com/watch?v=CpQeXnMRO-8
http://articles.sae.org/8707/
First please don't take it as a personal attack on your decision to buy a Sorento. It is a fine vehicle.
I said "misleading and inaccurate" but you could reach to that conclusion if you wish. I gave the benefit of the doubt to the Product Marketing folks because: 1. they need to spin their products and 2. the vast majority of them are non-technical people that does not fully understand the technical details of their products.
I am familiar with the Magna system as I was very interested in it when it came out and did my share of research on it. But it you take the time to search youtube you will find example of the Hyundai/Kia's "shortcomings". Still I was hoping to find out my concerns were unfounded and my expectations may have been higher because of the Magna system promise.
Now back to your challenge. The two examples you provided are actually supporting my point.
First the word "lock": the only way you can get a locking system is with a positive locking mechanism which requires gears and will never be fully achieved with a clutch pack (like Magna's system) or viscous couplings. Second there are only a handful of vehicles with a 4-wheel lock system: the Jeep Wrangler and not any Wrangler, just the Rubicon. Other examples are the Ram Power Wagon and Mercedes G-Wagen.
To get 4-wheel lock you need 3 locking axles: center, front and rear.
Magna tries to emulate only a center locking axle with limited success. The problem is that it overheats extremely quickly; it happened to me after trying to rock the Sorento forward-backward 2-3 times trying to get out of my parking spot. Another surprising fact was that some torque steer is noticeable accelerating from a stop in the snow even with the center "locker" on.
The main issue is with the AWD system not very capable of controlling wheel spin once it splits the torque between the front and rear axle. The instant one wheel start spinning you lose completely the contribution of that axle.