@Boris I'm with you regarding how it would be much simpler for those of us with single point emitters to have them defined by GPH, then being allowed to input how many of them are in a zone. For that matter I wouldn't mind if I even had to put in a GPH number for the whole zone.
My guess is that since the algorithms for watering are based on inches of water applied, the algorithm would need GPH translated to in/hr anyway for the algorithm to work. As you mentioned, the tool could do it for us, but without an algorithm change the area would need to be defined properly or our watering time would get screwed up. On a single point emitter that area calculation isn't so obvious. A 1ft x 1ft area is often recommended by Rachio for the estimate, but I disagree with that recommendation. Online calculators that I've found assume equally spaced grids of emitters, which isn't valid for single point emitters, or even if you have a few on a tree or shrub.
As it stands now, the only impact the area calculation has is to the water used. With a definition in in nozzles of GPH it would also affect watering duration. Of the two choices I would rather only have it the way it is now since it doesn't affect the watering time.
It seems to be a more complex problem than meets the eye, and perhaps that's why it hasn't been implemented? I do think it's a more significant point of confusion than Rachio might realize, as they may not be aware that many markets are dominated by our type of irrigation style. Three of my four zones are single point emitter setups. I also know they have a lot of development on their plate, so some things keep getting pushed off, without a deliberate attempt to ignore or deceive.
Having said all of this, the link below shows how I back calculated the area calculation in a single point emitter setup to get reasonable water estimates. I took the resulting area then plugged it back into the water usage equation and got the GPH/emitter * num_emitters value that I expected, so I think it works. You have to know how many gallons you want to put down, then set the PR accordingly. After that, do the back calculation.
I hope this helps, and thanks for bringing it up. It helps raise awareness to the issue.