The fact that the system was designed for a city really has no bearing on its deployment at WDW. The problem is the same, but the variables differ. In a city, stops might be consistently short, while the transit time (between stops) can vary widely due to traffic conditions. At WDW, the transit time will likely stay consistent while load/unload times might vary due to ECVs/passenger needs. Flexibility is built into the system-that’s what makes it different than just an old-fashioned route schedule.
The data is what makes the system smart and efficient. Without data, the system estimates what an average load time might be (average for time of day, time of year, etc.) and schedules each stop as a sort of window. In order to stay on schedule, the driver has to sit and wait for the scheduled departure time (even if the bus is loaded to capacity) and drive a predetermined speed. The only way the system can reliably predict when the bus will arrive at a stop is to know when it left the previous stop. This is what you observed during your research.
But when properly implemented, realtime GPS + guest tracking gets rid of the “window” idea and treats the problem of moving guests as a logistical one. It knows how many guests are waiting at a stop and where those guests are trying to go.
This allows buses to leave a stop when they reach capacity (or when there are no guests waiting to board). When the bus leaves a stop, the system knows when it will arrive at the next stop and can show that on the signage in real time. If the wait time for guests approaches the maximum allowable (whatever Disney determines), new buses can be deployed to that route to relieve the demand.
In this case, buses don’t necessarily need to follow the same route or stick to any certain schedule. Once the demand has been met, buses can be redeployed as needed or pulled out of service.