Yes, the IFPUV does use the route catalogue. Accepted and acknowledged FPLs ARE added to the route catalogue, routes flown as plotted in ETFMS (the flow management system) are also added.
We just tried the same route in IFPUV, FL390 gave 642nm vs 431 direct
FL 350 gave 583nm vs 431.
One of our FPL supervisors could only manage 559nm using his system plotting the route piece by piece, so IFPUV performed quite well. The zig-zag is all to do with the necessity to avoid military airspace in Fr@nce, there is a large military area just North of your dep aerodrome and another one in Reims ACC area just West of your destination. So not a shortcoming of the FPL system!
Do you complain that you cannot drive straight over roundabouts? Don't shoot the messenger!
Anyway, the best route between the two aerodromes mentioned that gives you climb to 350 (not 390) as fast as possible is North through Bordeaux, it is 583nm but probably more economical (only you will know that):
AFRIC G39 GAI UT186 PERIG UY156 ADABI UN858 VADOM UN874 BAMES UT191 PODEM UN873 VEKIN UZ173 ARVOL at FL350.
Play around with the FL, it makes a difference.
To all other posters, this service will not be repeated so don't start posting routes all over Europe!
