This is really only a problem if those planes are blocking an international arrival from using the gate. There's nothing wrong with an international departure going out of C1 or C2 versus C3, save for the 5 extra minutes of walking after shopping at duty free.

Also, some of the gates in C1/C2 will block adjacent gates if a widebody is there.
Yes and lots of studies. What isn't clear is the evidence that the current situation is bad. The B arrivals happen, in theory, because the 18 gates in C3 are occupied. With some needed for widebody departures during the European arrival bank (the 3 Asia departures noted in the chart above) and also the part where they cannot always just unload the plane and then tow it off the gate to make room for another arrival the C3 pier gets full some times.