Hi G.Paul,
So far I've only gone through a couple of belts. Because the belts are so long, there's a lot of abrasive area. Also, you shift it back and forth as you grind it away, so you spread the wear area out. If you drove it into the belt hard, then you'd blow out the belt.
I don't like the hole saw tube notchers: they don't work well if you have to remove another 1/8" or change the angle slightly to get a better fit. I've used hole saws in the vertical mill, and while they work, I've never been impressed with their performance vs the abrasive tube notcher.
Some guys will just use an angle grinder with a cut-off wheel and clean it up with a flapper disc and swear by it... I have done that too, and it works okay for small tubes, like 1" or smaller going onto larger tubes. But for the best fit-up, the abrasive tube notcher gives the best fit and best finish.