I'm perplexed by the oft repeated notion that green grit wheels are no use for sharpening carbide.
They not as good as diamond wheels. Does that make them "of no use"?
I don't bother setting up a diamond wheel to sharpen, say, a brazed carbide lathe tool for roughing interrupted cuts hard material. Or for (as I often do) modifying a masonry drill for hard metal drilling.
Green grit is just FINE for jobs like this, and preferable to diamond IMHO in cases where the steel substrate will contact the grinding wheel (and consequently greatly reduce the life of any diamond wheel not specifically targetted towards steel grinding: slow speed, coolant....)
It's a bit like saying manual machine tools are "of no use" since the advent of CNC.
There was a time, thanks presumably to the genius of de Beers, where diamond wheels (at least in the semi third world conditions of our local industry) were pretty much something you read about rather than owned, the Lamborghini Miura to our Lotus Sevens and Mini Cooper Ss.
I'm talking about during the carbide era (I'm old, but not exactly a centenarian)
... the lucky few would tickle up the resulting edge with a pocket diamond hone (even these used to cost a prince's ransom) and be away laughing. The rest of us would be perfectly satisfied with the off-stone finish.
(Chorus from offstage: Looxury! You 'ad a green grit wheel? We had to roob tools on concrete path wit' bare 'ands!)