I suspect a bit of both. As we usually travel during slower times, I have always found the buses to be adequate, but on our last 2 trips, buses have definitely been a little better than adequate under the "demand" system.
They are truly trying to improve the system and are working diligently to accomplish that task, but Diseny does realize that the bus system has a limit as to how many more it can handle.
With 2 more resorts coming online in the next year year (Pop Century and BCV), plus the recent addition of AKL to the mix, the current system is certainly being stressed and stretched to it's limit. Disney continues to look at monorail or light rail expansion to significantly improve guest transport.
Any further bus expansion will test the roadway congestion limits, something which the system truly doesn't need. Something definitely has to change for the future.
Stay Tuned!