The addition of CC’s will help, as been already suggested. The stiffness may also be helped with midi resolution. BiaB is only 120 PPQ, not enough IMHO. I would bring the midi file into RB or another DAW, set the midi resolution to 960 PPQ and adjust some of the notes + or – a few ticks. If your DAW does not have randomization then check out hitsquad.com and look for a free randomization VST.

Good luck!

Whenever I get something stuck in the back of my throat, I dislodge it by drinking a beer.
It's called the Heineken Maneuver.

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware