I always thought my 919 was a pretty smooth-running engine. My other two bikes are single cylinder 650's, so, anything is smoother than those I suppose. Anyway, I always wondered why my hands still got numb fairly quickly on the 919, because I had my 650's feeling much smoother by installing Vibranators and handguards (they are dual-sports). I took my bike by the shop that makes Vibranators, and they made me a set for the 919.
They took out the stock inserts...what pieces of crap they are. They installed some of these tuned mass damper inserts, and BOOM...the handlebars are DEAD! Well, not totally...from 2100-2400 rpm, I think they vibrate more than before, but, it's like a switch is flipped at about 2500 rpm-up to redline. I mean NO vibration! The weird thing is, I suddenly felt a lot of vibration in the foot pegs. Of course, the footpeg vibration was always there, I just never felt it because of the vibrations I was picking up in my hands.
If anyone else has vibration problems in their hands on this bike, or any other bike, I'd recommend trying these. They make them for many different bikes, and are adding new models weekly. All this time I knew I wasn't gripping the bar tightly, I just assumed it was something else, like too much weight on my hands. Such a simple fix...