The Model X uses 22.93 kWh/100 km. Electricity is € .31 / KWH. 22.93 * .31 = € 7.1083 / 100 km
The GLC 200d uses 5.2 L/100 km (best efficiency). Diesel is € 1.266/L. 5.2 * 1.266 = € 6.5832 / 100 km
So yea in DE it may be more cost beneficial to drive diesel than electric. If you get a GLC 300 using gasoline it goes up to € 9.798 / 100 km.