The problem was that the software for defining the arcs that the paint gun needed to move through was, well, a bit shit. It always produced inconsistent thicknesses.
Obviously, prior to getting the arm, the props were painted by hand. There was this one chap who was just incredible. He'd move his arm in a motion that followed the contours of the prop perfectly but at such a consistent pace that the paint was laid down beautifully. In the end they gave up with the software and just motion captured his arm movements so they could replicate it. It wasn't as good as he was but was close enough.
BTW my job there was to design jigs for a batch of Spitfire blades that they were building. Someone had commissioned new 'planes to go with some Merlins that had been found at Rolls (if I recall correctly). I worked at Dowty who had made the original blades and landing gear so we were making them from the original blueprints. Was a lot of fun.
A corollary to the labour cost also seems to be a reduction in high end craft skills. Modern houses don't have the features that require high end skills as they're too expensive so there's less demand for those skills. Another anecdote: it took us ages to find a plasterer who could do the ceiling in one of the bedrooms as the cornering was so complex and most refused to quote. Eventually, one of them put us in contact with a retired gentleman who did the work (at a quite reasonable price considering). Watching him work was amazing.
The only time I recall being more impressed was, many years ago, seeing a spray painter paint a propeller as a template for the robot. It was a bit like watching dancing but to a micron (or so) tolerance. Masterful.