AWD and 4WD are also marketing terms rather than regulated in any way. In general you're right, but to be safe, always check what type of transfer case you're actually dealing with. Some "4WD" cars these days are AWD with super clever electronical controls for off road usage.

AWD systems use a viscous clutch

In my experience, that's rare. Most AWD systems that I've seen use an open differential with no viscous coupler or locker of any kind. The '94 - '97 Toyota Land Cruiser (w/ ABS) in the US market used a viscous coupler, and Toyota called it "full-time 4wd". It also locked the transfer case in low range. To my knowledge, this was a really unusual configuration. They discontinued the viscous coupler after that, instead switching to their ATRAC traction management that used individual application of brakes to prevent wheel spin. Most of the Jeep SUVs in the last ~30 years, to my knowledge, used an entirely open center differential in AWD models.

It seems like modern, CUV AWD systems are usually FWD with computer controlled engagement of rear tires.

The exact meaning of "4WD" seems to depend on manufacturer. Toyota's 4WD works fine on hard surfaces because the differentials are normally open, which makes it a lot more like AWD. The center differential needs to be locked for it to behave like your described.

Or in my case off until needed.

Car's a hybrid so runs in FWD until it thinks you need the rear electric motors to keep you on the road then it's AWD.

Eh, oversimplification. AWD systems can and do get used offroad pretty often. They're not quite as good as 4WD in some specific situations, but AWD is still better than 2WD in basically every offroad situation, and it's good enough to get the job done most of the time, for mild offroading. If you're doing serious rock crawling or going through very deep soft sand, mud, or snow, 4WD will likely be better than AWD. But for tackling your average trail or poorly maintained dirt road, AWD will do fine.