Yeah, the slow generation of the RT's in RB is a problem. We're dealing with really large audio files here and that simply sucks up the processing power. Biab is the one that has the fast generation option. This was just implemented for this past Xmas. Many times what happens is the two programs leapfrog each other so that enhancement may make it into the next version of RB. For now, try to complete your arrangement first and start off in Biab and then drag and drop the tracks into RB later if that turns out to be a faster way to work. Other than that, I don't have any other answers for you.
For now the only real answer to this is a killer fast computer. We all talk about how you can get a pretty nice system for under $1,000 but if you go onto Newegg or Tiger Direct and check out the high end systems they still run around $2,500. I'm sure one of those systems will generate all those tracks fast but who wants to spend that kind of dough on a PC?
Btw, I discovered a few years ago that other DAW's are not any faster than RB even though at first it appears they are. What happens is they all use a ton of temp files that store all your edits and it seems like the workflow is way faster but when you're done and you go to save everything it can take 10-15 minutes to flush out all those temp files in order to save everything. RB does that flushing of those temp files as you go along so the workflow seems slower but the saving at the end is much faster. Six of one....

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.