France had eased into a 17-0 lead with tries from Jerome Thion and Pierre Mignoni before Hook struck.
And they sealed the win after the interval with further tries from the powerful winger Aurelien Rougerie and replacement hooker Sebastien Bruno, who scored with the final play of the game.
Jenkins said: "The difference today was not the way we have played but between the ability to be clinical in the finishing process.
"There was a lot of creative effort from us but not the clinical edge we need to score tries against teams like France.
"We have made improvements. We will grow as a team but the difference today was that we have seen a side who have shown a clinical edge and that is something we have to grow into our game.
"The physicality was up another level and the way you have to react in the physical contact area magnifies your accuracy.
"We have talked positively in the changing rooms. We are hugely disappointed but it is not the World Cup yet.
"France are the third best team in the world but we have been competitive in every aspect apart from finishing."
The matches have run out now but Jenkins is confident Wales can develop in training between now and their World Cup opener against Canada on September 9.
"We have made improvements in training in the last couple of weeks. There is an honesty among the players, we will identify where we are disappointed and where we have to work.
"We have learned lessons from France. We are not where they are. The next challenge we have got is Canada and it is a huge game for us."
Jenkins also allayed fears over captain Gareth Thomas, who was stretchered off at the end.
"He was exhausted. He has got 20 stitches in his face in a cut under his eye, a cut over his eye and a cut on the chin. There are no long-term problems."
Dwayne Peel (knee), Duncan Jones (shoulder) and Chris Horsman (shoulder) all picked up knocks but are not thought to be too serious.