The original intent of FP+ - according to the presentation given to the board - was based on the finding that guests who used FP Classic were more satisfied than those who didn't.
Disney was willing to accept a small increase in overall standby wait times in order to capture that extra satisfaction.
I think they landed on 3 as the number of FastPass+ reservations by looking at each park's available ride capacity at something like the 80% attendance threshold.
It was also intended to avoid future investments in park attractions, since “the more we build, the larger the crowds grow anyway.” That was part of the presentation when Disney trained CMs. Tbh, it’s true from a bottom-line business perspective; yet Disney parks used to consider more than that.
The team partly sold the board on FP+ by talking up guest satisfaction numbers, but it was
also always a shell game to move crowds around and minimize expensive new rides and lands—all of which they ended up having to build anyway. Office-based CMs were welcome to sign up to little teams to help test and implement the system. It was bluntly, flatly described to us as a way to manage crowds and save on operating costs. The language was part of the official onboarding. It was in paperwork and a PPT deck. Nobody pretended it was about the guest experience other than a vague promise that one day in the future, guests could plan their entire dining and ride times “like a cruise ship.”
It seems — and this is conjecture — that the NextGen team sold the Disney board on an idealized, blue-sky, dreamy version of FP+, and were more blunt (honest?) when testing and training CMs on the system.
EDIT: These forums have thousands of posts about FP+, and regardless of whether people like it, love it, or hate it, everyone agrees (or
admits) the overall resort experience has become hyper-scheduled and less relaxing as a result. Queue lengths at have been artificially inflated at crowd-crunching omnimovers and boat rides, quick-service restaurants often operate with purposefully limited windows and dining rooms, and the system was never duplicated at any other resort as intended. I guess the only question left to ask is whether Disney plans to fix the system at WDW.