Nice composition but a lot of tonal banding due to a number of things, the foremost is that you converted from RGB to Gray. RGB has a nearly unlimited palette whereas Gray, has about 256 values available.
Taking it into Photoshop, I reassigned it as an RGB image, then took it back to camera raw and added a bit of dehazing and clarity, knocked back the blacks a bit and knocked down the highlights significantly. Doing so smoothed out the banding, increased the depth yet left the two gentlemen pretty much the same.
You may not use PS but the same can be done in LR (I think). I always tell everyone, "if its gray, go away." RGB makes for awesome B&W images.