Even real life alliance purpose is just codesharing flights, and other things like lounge sharing and miles redemption. Alliance contribution towards airline is just adding more pax in their flights with of course fare paid towards operating airline and small portion of fare towards "booking" airline as fee. In fact, airline still compete even through in same alliance.
In my country, flight from Kuala Lumpur(KUL) to Heathrow(LHR) has 2 flight, both almost same time which 23:00(MAS) and 23:30(BAW). Both are under OneWorld Alliance and I can book both flight on either MAS or BAW website. Been thinking why not share flight rather than waste cost for both airline eventhough my flag carrier MAS is bleeding money for years.
Passenger may book ticket SIN to MAA from your airline website, stated codesharing flight with fare slightly higher compared to direct flight provided by your airline(if available) or your competitor. Same as above case, fare will sum up from 3 which is SIN-BOM(fare to you), BOM-MAA(fare to alliance partner) and BOM-MAA(codeshare fee paid to you).
I agree that new feature updates should be adding more pax in your flight as codesharing pax which should be other type of demand and not from demand in route planning. Or maybe, pax demand should update to be same as cargo demand, in which pax from Rural airport(R) take flight to Bigger airport(B) in its country before flying to Other country(O). This will boost pax demand between R-B and B-O. Once direct flight is available between R-O, demand between B-O and R-B reduced again to balance.