Ohh no, I have just removed my barrel and after years of using supermarket cheapest full synthetic 5W-40 oil, idling at low revs cutting through miles of rush hour traffic jams for the past 3 years at low revs as well, it would suggest that the standard EN steel cam would be a nice piece of tube - strangely not, it is not perfect, the right hand exhaust lobe has started to wear and so has the follower the other lobes are like new and the followers show only the normal pattern, these were refaced when the cam was put in 18 years ago. This would suggest that the oil is not blame, nor are low revs.
It is well known premature cam wear has occurred on steel and chill cast cams, made even more frustrating by the like of my cam that 3 of the 4 lobes are like the day it was installed. If it was contamination from above then the adjacent lobe and follower would be affected, it's not, so that theory is discounted. If it was the material then more than one lobe would be expected to fail, they haven't So the oil, low revs, contamination and material are off the hook.
Springs, the head was replaced in 2016, new valves and standard springs were fitted, if it was the springs then surely it would affect another lobe, again it hasn't so I doubt the springs but not entirely because of what I found, the remaining valve tips show wear on the tip where the adjuster runs, the valve tip on the worn lobe side shows nothing not even any rubbing. It looks very much like there has been insufficient spring pressure on this exhaust side, and thus the reason for not even a rub mark - could this be the reason?
Installation, possibly - being a head fitted with standard items and running on a standard cam I did not check for coil bound, but being on the exhaust side the remaining spring travel at full lift is more generous than the inlet, so I doubt this is a factor, as I would expected similar on the opposite side, also an imprint or wear mark on the valve tip.
I am now suspecting spring or things that can affect spring pressure and will check a few more things on that failed lobe side, valve stem collet recess height, fitted valve seat height etc and compare it to the good side.
This leaves very few possible causes of premature cam wear, irrespective of material and type, loss of lubrication, installation, dimensional changes relating to the head, machining and fitting of valve seats.
Strangely, I am now in the position that I can test a few things, and thrash the bike to Austria later in the summer, or fit my spare engine that is built up with standard chill cast cam and test that.