What he said. Very good synopsis, Noel. Since you covered most of the good stuff, here's some bad or not so bad depending. The biggest one is the endings. Biab or RB will both implement holding a chord or note just fine when it's midi but the Real Tracks are audio files. It's impossible to take a quick strum or piano chord and make it extend out 3 or 6 beats like an ending. There's a lot of complaints about this but right now there's nothing that can be done except to do that last chord in midi using a good sounding synth and hope it blends well enough with the sound of the Real Track. Other than that, there are programmed endings for the styles, they just may not be what you're looking for.
The other thing is trying to create a real arrangement with breaks, definite bass lines, drum fills stuff like that. You're limited with what you can do just using the RT's or RD's again because they are prerecorded tracks. A question that comes up over and over is why can't I use the Sax or Guitar soloist RT to play my own solo or melody part? The program can take an RT soloist and chop it up and put it back together in interesting ways using your chord changes but it's not going to play your own part back note for note. You have to do that with midi.
Those demo's are real, no funny stuff going on. As you noted, a lot of them really sound fantastic. You can load most of these demo songs into Real Band and play with them yourself.
In spite of these limitations, these tracks are awesome and I wouldn't be without them.

Bob

Biab/RB latest build, Win 11 Pro, Ryzen 5 5600 G, 512 Gig SSD, 16 Gigs Ram, Steinberg UR22 MkII, Roland Sonic Cell, Kurzweil PC3, Hammond SK1, Korg PA3XPro, Garritan JABB, Hypercanvas, Sampletank 3, more.