The air inside is already spinning, the holes at the exhaust aren't the blades like for a squirrel cage fan. They're angled in that manner to reduce the negative influence of the air outside as each hole starts at zero speed relative to the outside world when the hole is lined up with the tire contact patch, and accelerates in an arc to it's fatest speed 180º from there and decelerates back to zero on the way back down the other half of the arc. The mod isn't for the rated power crew, but instead for those running higher power and speeds, and a 20cm diameter centrifugal blower can move a lot of air even at just a few hundred rpm, and relatively small flow makes a huge difference compared to the stock sealed motor with hot air inside that must transfer the heat through the outer shell to the outside world.
Of course there's nothing wrong with scoop-like blades at the intake other than the increased potential of scooping grit and sand into the motor. I left my option open to doing exactly that on the first one I ventilated in case the cooling effect fell short. It worked well enough for me that I haven't bothered with scoops.
If my latest version falls short, because I want to take it to pretty extreme power, the motor is too difficult after my wire harness mod to remove the intake cover, so instead I plan to add one large stationary scoop to the bike frame that would funnel air toward the ring of intake holes. This would increase the air pressure there outside of the intake holes, and prevent air from flowing fast by the holes. Both of those effects should help create more flow without increasing the chances of small debris entering too much.
Doubters can doubt all they want, but when I've got identical motors, one sealed and the other not, running at the same voltage in the same size wheel at the same speeds, there is no doubt. Loaded down only enough to push consumption at about 70wh/mile the sealed motor gets hot enough to concern me because I can't hold my fingers on the surface between the spoke flanges for more than a few seconds. Loaded down much more for the same climb, the ventilated motor consumed 167wh/mile, and at the top was only slightly warm between the spoke flanges. We waited for a minute or two and the temp didn't rise and we couldn't feel hot air rising from the upper vents, so the stator couldn't have been terribly hot either.
That's proof enough for me, and actually better than only measuring and comparing stator temps, because that's just part of the system and the magnets have a lower heat threshold than the windings. Better cooling won't save a motor pushed too far into stator saturation, or bogged down to too low a speed on hills, so avoid those situations.