true, there is 3 WD
the rear axle is solid 2WD, the front has a diff because of the cornering . in simple 4WD no locking, like he said when you hit a slippery surface or loose rock climbing, one front will spin twice as fast and the other will jst stop.

same as any 2Wd pick up truck,... when on regular road both rear wheels will push just fine, but put it to a bit extreme, example a wet boat lunch ramp , or snow or ice, and one rear wheel spin like crazy , the other will stand still.
they worked around it by giving it a limited slip diff which will engage when there is a given RPM difference between the 2 sides.
then it should lock up or slipp less.
these are achived by clutch plates or centrifugal weights and locking pins. I had a chevy caprice cop style car which had a rear good real difflock till the clutch plates started wearing and it became a 1 wheel drive. (not good in snow )

bottom line , yamaha has a cool system which allows free wheeling in the front - in 2wd mode ,
which = super easy steering, 4wd when needed , and locked front 4wd when things get really nasty.
the best setup.

polaris AWD is not bad , but I would preffer not to loose traction... waiting for the 20 % wheel speed different to kick in the AWD.
on a nasty down hill I love the way the 4 wheel +engine braking holds my kodiak, (grizz the same ) normally no need to use brakes.