A-B-C-D-A routes are in general ineffective. For smaller cities tho, its usefull as the line can cover more area and completes it faster. Therefore u need less busses. But for larger routes, in my expirience, busses fill up in the first couple of busstops, so people waiting at later busstops are continuesly waiting for a full bus… As people at the first busstop who enter the bus, need to travel the whole line in order to get to the railroadstation.
My view 🙂
Oh and that bug with looping busses also occurs when the city grows. When a road is connected to the road a bus is driving on, it randomly gets put on another road which is not even part of the line its driving. Very weird… But they will keep following the line correctly. Altho this messes up the time between busses which is very hard and time-consuming to reach.