Originally Posted by
CalFlyer
No surprise at all. In my experience, it is always the airline that operates the metal that has the cheapest fares on a direct route. Cannot think of an example where a codeshare airline had the cheapest rates. I have experienced that many times, also the other way round (where e.g. KE is the operating carrier and EK sells it under their flight number - tremendous fare difference).
You are probably correct in so far as that is what the airlines want... but there are definitely occasional interesting cases where it is cheaper to buy one carrier's flight on another carrier's code. I think MK/EK to MRU used be one of them.