Once you go back and forth a few times between Reaper and RB (to add another part, or change a part you generated previously) you may adjust this opinion. Or you may find that getting the 'basic idea' down in BB (style/chords/tempo) is quick, but then you can have more control finishing up the generating/arranging in RB.
Then comes the decision of 'when do I need to leave RB and go to another DAW?'.

That's the line that fluctuates for a lot of users.
I grew up on PT, so the workflow in RB and knowledge of how it works allows me to stay there for most if not all of the project. Do whatever fits and feels comfortable for you. You're farther than a lot of users already. If you understand what RB does, you'll know when you want to use it. Many BB users never even open RB!

I do not work here, but the benefits are still awesome
Make your sound your own!