There may be something out of whack that is causing the damage to your sprag clutch. However, without further information, it's difficult to diagnose. But I can tell you that the electric starter system on Norton Commandos is fairly delicate. In fact many people will remove the starter rather than repair it when it fails. And it tends to fail often.
Electric-start-owners that do retain the starter tend to use it sparingly and judicioulsy. For instance, they will kick start the bike when cold and reserve the starter only for the relatively easy hot starts.
If you do decide to @#%-can your electric starter system, be sure to save the end caps from the starter motor. These can be used to make a clean-looking cap to plug off the gaping hole in the inner primary cover were the starter used to live.
If you are destroying your sprag from kickback, I would try to eliminate the kickback first. This is usually timing. As Dynodave has said many times, the analog Boyer can be a problem if the voltage drops below 10.8. That said, I know a couple people who use an analog Boyer and have had no problem. I did on my cafe racer for a while, but switched to a Rita and have had no kickback problems since.
When you are certain that you have proper timing and the engine starts easily with the kicker (no kickback), then pay close attention to the "anti-kickback device". This is a cupped spring washer (bellville washer) which is designed to slip if the engine kicks back, saving the fragile sprag clutch. Make sure this assembly has not been drawn up tight and will slip. I had to draw it up tight on my 10.5:1 850 or the starter would spin wihout spinning the engine. Of course the price I pay is no kickback protection. That's when I realized the Rita works better!
With the cost of new sprag clutches, you want to make sure the kickback assembly works.