It truly is sometimes hit or miss and that is not necessarily a fault of the system but just luck in catching a bus as it arrives to the bus stop. We call it Bus Karma.
As you walk to the bus stop you see your bus approaching then you have good bus Karma, if as you approach the bus stop you see your bus driving off and you have to wait for it to go to the stops at SSR and then to the park and back yes it can be at least 30 mins.
Even with a 30 min. wait I seriously doubt anyone saves time driving to the MK, parking in the lot, catching the tram, riding the monorail or ferry over any Disney Bus, it's all perception in that because you are moving in your car you are saving time.
Personally I find sitting at the bus stops pleasant and have had some nice conversations with fellow bus stop guests. It is all in how you look at the experience.