The Quality of the exhaust valves that can be bought these days (and for many years), has a very low wear resistance, in my experience anyway. All are made in stainless and some are even called diamond (must be the softest diamond ever). I have been doing a lot of miles through the years on my BSA, this last summer 10500km ( ca 6500 miles) and every time I service the cyl.head ( ca 30 000km) there will be badly pitted ex valves.
The valve to the left in the picture is one example of such pitting. Valve nr.2 has had a groove grinded and hard wearing bronze welded on (5 - 600 Brinell), valve nr.3 the bronze seat is grinded and ready for use.
I have done similar many years and ca 30 000 km ago in my old H...a and the wear of these valves are almost none. When also having hard type seats in the cyl.head the lifetime of valve and seats will be very much longer. The same type of bronze can also be welded on camfollowers, the wear resistance being excellent.
The LH picture is from the H...a workshop manual
showing stellite welded on, which seems to be H...a practice.