For me it's a workflow progression system.
Use BiaB as needed to design a song.
Use RB to generate sections, edit tracks, re-render DXi tracks with different synths, record additional tracks, start on the mix.
Many times I just finish in RB from there. If I like what I'm getting I just keep on tracking.
If I need to do something RB doesn't do I'll jump to whatever other solution I have to get the job done. No qualms there.
Point is, if I go to another DAW right away from BiaB, I give up a lot of options that RB retains for me until further down the road. Can't do a lot of work in Reaper, then regenerate a new bridge ... without the D&D dance a few times. That option to regenerate is priceless sometimes. I try to stay in RB as long as I can, even if I know I am eventually going elsewhere fo some certain thing.
Just my workflow here. Tryin' to be efficient.
BTW, a bunch of the Reaper VST's work in RB. I happen to like them, so there are ways to even combine some aspects..

As to whether RB is limited in some ways. Yes- RB doesn't do some things that Reaper does well Running VSTi plugins that require a tempo lock for processing the sound is one. Other ASIO aspects are another.
Then again, as I mentioned; the regenerate thing, along with a couple others are unique to RB.
It's all good.. or if it sounds good it is good. One of those.