Actually it is not that bad with the Z fares within Europe. It costs around 600 EUR for 4 segments in Z that earn 1875-3000 miles per segment.
So with an average of 2000 qualifying miles on AF per flight at 150 average cost, you reach 360k miles with 180 segments at 150 EUR, so 27000 EUR in 2 years. Now let's see if the benefits are worth it. If they give P service for J (long haul?) flights, then that could be interesting for the regular J flyer.