I agree, the Torsen is probably one of the best features about this truck. I disagree with you fundamentally, however. Your understanding of the torsen is generally correct but with one very key flaw that you mention several times yourself; a Torsen REQUIRES some kind of resistance (i.e. TORque SENsing) in order to work correctly, this is why it is so great in road cars (Audi) and even offroad on generally grippy surfaces.
Asphalt is almost (for the sake of argument) uniformly grippy so it stands to reason that on at least one corner, some tire has substantially more grip than the other. The Torsen "senses" this and routes power towards this resistance, rather than away, as in an open diff. If asphalt is uniformly grippy, a sand dune is as close as you can get to uniformly UN-grippy. When a slight resistance is felt at any corner and the torsen attempts to route torque that direction, the wheel with "grip" just digs itself in. In a deep-sand situation, the torsen behaves just like an open diff, not because it is bad, but because the necessary torque to make it work just isn't there. In these cases, and there are only a handful of traction surfaces that can defeat an un-locked torsen, the 50/50 lockup is better because now instead of 3 open diffs, you only have 2. This is why our truck is configured like it is, electronic nannies (that simulate traction) and all.
I agree that these electronic nannies can be bothersome in slick, icy or muddy situations where wheel spin is necessary and wont dig you in (unlike sand). I think Toyota ultimately realized this as well which is why they gave owners on 07+ T4R's the ability to turn all these gizmo's off. I have run deep sand with all the electronics off in 4HI unlocked and it was a constant momentum battle, every tire seemed to alternate from digging itself in to just plowing as the torsen kept rerouting torque. With the center diff locked, things were a lot more sorted out and each wheel pretty much had the same lack of traction so no one tire every really spun. It is for this rather long explanation, and the fact that its all really just theory and conjecture, that Toyota most likely added the multi-terrain select feature to the new Trail Editions and Land Cruiser's. You look out the window and spin the dial to a terrain setting like what you see and let the truck figure it out. How well this appeals to Torsen / 4WD nerds like us lot remains to be seen. Cheers!