You may have read too much Herman Kahn.  I'm not sure "escalation ladders" really work...Nuclear Deterrence works at very low levels.  The US had UNDISPUTED Strategic nuclear dominance, and theatre nuclear dominance during the Cuban Missile Crisis and STILL was concerned about the loss of coastal cities, from nuclear torpedo strikes....

 

France's two SSBN's pretty much guarantee France's ability to resist nuclear blackmail.  I doubt the US or Russia or any nation is willing to lose their equivalent of New York, Chicago, Boston and Atlanta for anything less than national survival.  And France can deliver that kind of destruction.  That's really all nuclear weapons are good for, threatening a Holocaust in response to a Holocaust...they are extremely hard to use otherwise.

 

But again this is less about the Force de Frappe and Nuclear Deterrence and more about France's ability to intervene in a sustained, conventional manner on a global scale.  And I think it is still safe to say that France has more capacity than the UK and is second only to the US.  The CdG may not be all that, but it's more than most nations possess.