I've owned a Tesla for nearly 3 years, and I have no idea how to do that via the steering wheel controls. I'll dork around with the interface when I get back in my car after work today to try to figure that out. But evidently at least for me, feature discovery is half the challenge, no matter how easy it is once you've discovered it.
That video tutorial is now outdated since there has been many UI improvements, but the steps should still be the same.
Terrible idea? It's the best thing since sliced iPhone. Keep in mind that the "car" is usually driving itself; that's a much higher level of solving the "silly human takes eyes and hands off road" problem, which makes what Mazda is doing seem, frankly, short-sighted (disclosure: although a Honda/BMW/Tesla fan, I've always secretly cheered for Mazda because I like their driving "DNA," and if I ever buy another non-EV again it might just be an MX-5 NA or NB for autox/track use). Now, of course, they're _currently_ not in the same league, but this stuff is getting cheaper (technology! heck yeah!) and these changes should be a look toward the future. All of that said, I don't feel like there's anything wrong with the move they're making, just, again, doesn't seem terribly forward-looking -- other than that, it's perfectly fine.
I'm doing web searches for this right now and not finding anything, either for Model 3 or Model S, or just Tesla in general.
Where do they hide this information?
This is a very common misconception. You CAN adjust the A/C via the steering wheel buttons, turn it off, control the fan speed etc. It's very intuitive.
In fact, you can this for most of the common controls. The settings on the touch screen are mostly for things that you only really bother with once like saving your seat-position and personal settings to your driver profile.