Interesting observations about the apparent 'slowness' of the steering. I can only assume it is caused by lifting the height of the track rods, thus enlarging, by a very small margin, the distance the steering arm has to travel when movement is input at the steering wheel end.
I cannot think of any other cause. Other people who have only had the risers fitted say the same thing, yet with the Empire wishbone kit fitted as well, this does not seem to be the case, on my car at least. I can also play around with camber and castor change, which is impossible with the standard setup with Morgan 'comfort' risers alone.