Differential, not just more rudder.
Actually the reason for differential instead of mixing rudder with the controls is mostly for simplicity. And the reason they do it at all instead of not bothering as with older planes is to reduce spin accidents.
An airplane coming in for a landing that has the ailerons cranked into the cross wind and then needs rudder to kill the adverse yaw and resulting slip/skid has a number of things going against it. Roughly speaking, it's envelope has been reduced in a number of things by all that's wrong with it. It's not a very efficient design in certain areas and is generate excessive drag to fly the pilot's chosen course. Solve some of those problems and the airplane flies more efficiently.
There is no problem with using rudder to kill the adverse yaw. The problem is that many pilots do not do it correctly at all times. You seem to think there is a lot of drag when the rudder is cranked over a few degrees, but actually it is fairly small. The large drag you are thinking of is uncorrected yaw, from the side of the fuse facing th wing. Yes it is better to use differantial aileron for several reasons. But for our models they really don't exist. And with a high wing high life surface with dihedral you will get improved roll rate with rudder correction than with differantial aileron.