When he was King of France in OTL, Louis XVIII does seem to have been a sensible ruler who realised that the times were changing and that the monarchy needed to change with it. On his death his brother Charles X tried to turn back time and lost his throne as a consequence. If, as per ATL, Louis becomes King in say 1780 he might have had time to turn things around in France and either prevent or at least delay the revolution. He seems to have been brighter and most self confident than Louis XVI and this could have led to him trying to tackle Frances's problems head on, perhaps with some success.