Playamar2
The short answer is that yes, there is often a cost saving from a longer routing but avoiding overflying more expensive countries.
Airlines have software that will provide the true cost of a sector on various routings, taking account of fuel and aircraft costs, wind conditions and overflight charges. The flight planner often will have to balance the reduced cost against any impact to on time performance with longer flight times. The savings on the oceanic routing down to the Canaries can be huge.
But this also applies to the whole of Europe, flying to/from places like Greece, Cyprus and Turkey airlines will often fly slightly longer routings over cheaper countries to save overall cost.
This isn’t a new thing, the airline I worked for 15 years ago was doing it using software supplied by Jeppesen.