CO2 is at least partially a liquid when it's at high pressure in the cartridges. So the CO2 expands into way more gas volume than a similar cartridge with just compressed air in it.

The newer style screw-on CO2 inflators are much less prone to goofs and bad technique. They reliably fill the tires instead of spraying CO2 all over. The usual recommendation is to carry a Genuine Innovations Air Chuck. It's extremely small, too. And there's other similar inflators available.

Yes, the full size frame pumps are very fast. Too bad that newer bike frames often don't have good mounting locations for them.

I counted 200 pumping strokes on my Topeak Mini Morph pump, and that was just to get a 25mm tire up to rideable pressures, around 70 to 80 psi. Tedious, but it never runs out of air. I only bring it as a backup on long solo rides now. CO2 and one spare tube is enough for most of my riding -- I only get a couple of flats a year.