I agree with this. If you observe the way that fat renders out of a piece of meat then you'll also observe that most of the fat from the cap has to basically roll right off and into your drip pan. Whether it is on the top or the bottom makes little difference. Thinking about it from experience - where do you want bark? On the meat itself, not on the biggest piece of fat, so - it makes a lot of sense to do it fat cap down. Most of your bark is going to be on the top and sides of the meat, not on the part that is on the grate.
This weekend I did a pork butt on my BGE that had a lot of the fat cap trimmed, so while I did it fat cap up, there really wasn't much of one there. It was one of the best "hot and fast" butts I have ever done. Low and slow is better / more moist, but you can get pretty OK pork butt going hot and fast.
I don't have any gadgets with the egg. No fan, no regulator, no probe. I started this one about 9:30 AM for a 6:30 dinner. The egg was about 270-280 dome temp so on the grate was probably something like 325. Didn't wrap it through the stall. In the last 4 hours at 1:30, 2:30, 3:30 and 4:30, I sprayed it with ACV. Took it off around 195 degrees at about 5:30PM and let it rest for an hour before pulling at 6:30.
Was about the best pork butt I've ever gotten in 7 hrs.
Some people who are into BBQ get super obsessed with super consistent grill temperatures, etc. With pork butt I assert that it doesn't matter. I have made a lot of great pork butt on my green egg without any fan/regulator and without a probe. I'm in triple digits on pork butts on my BGE - just me, the grill, and an instant read thermometer. Many temperature fluctuations that would be "unacceptable" to some enthusiasts. Just let it go long enough and rest it and it will be good. I've only had one that I didn't like. It was too smoky and I overdid it. It has been a while. I think on this one I let it go overnight and woke up to a grill that had gotten too hot.
I'm excited about my KK getting here b/c it will be even easier to regulate temperature without any gadgets. But I probably will also invest in some gadgets. But you don't need anything but you and your KK and an instant read thermometer to make a good pork butt. Pork butt is very, very forgiving. (I cannot claim all the credit for my product).