What makes you think Real Band doesn't do midi regeneration using Biab styles? It most certainly does, that's one of the very big reasons to use it. I know it's very easy to confuse Real Tracks with the midi part since PG makes a very big deal about using the RT's. If you have a good sounding midi synth like the Ketron SD2, the Roland Sonic Cell or any other good synth, those midi tracks can sound almost as good as the RT's but you have all the control that midi gives you.
In RB, all you do is first pick a style, right click any empty track, pick midi, pick the instrument and generate the track. You can then do the same thing using the next empty track but try a different style using the same instrument. Doing this you can create multiple versions of the same part like the guitar. You might like one style for the verse, another style for the chorus, another for a bridge etc, etc. No problem at all if you only want to regenerate just part of a song but keep the rest because each track stands on it's own. They don't regenerate automatically. You can do this using all 48 tracks if you want. Then when you're finished tracking all your experiments, start picking and choosing the parts you want to keep and delete the rest. You can create some very cool stuff this way. Much more flexible that Biab alone. All this works using the RT/RD's too so you can mix several RT's or RD's along with midi tracks. Remember, everything is on it's own track including separate midi drum kit parts if that's what you want. Real Drums are a stereo file so you can't separate those.
Real Band is PG Music's way of addressing all these issues with Biab. They decided it was better to do it using a separate program instead of adding more and more stuff to Biab. Biab is complex enough already and is designed for a somewhat different user.

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.