First of all, where did you get the fact that L'automotive sportive is the truth maker? Does that website is what defines what is and what is not a classic? Or even "Tour Auto", an automotive EVENT, keep your eye in the "Event", which means specific rules. So is "Le Mans Classic". It's an event, not a classic car guide. "Le Mans Classic" is not much different of Goodwood Revival, just an event, not a definition.
Drop random links you find on internet, or links from blogs you follow do not make you right. And no, it is not "only" Insurance that gets cheaper or more expensive, go take a read about it.
If you take a read somewhere else, over pretty much any place in internet, you will find the same answer for this question. And the answer is always age. What makes or not a car, a "classic" car is their age. The age may vary from country to country, club to club.
Classic Car Club of America doesn't consider anything after 1948 a classic. But Antique Automobile Club of America considers anything between 25-50 years old to be a classic, and older than 50, it's antique.
Take a read on this or this, if you actually want to read, instead of just type gibberish on this thread.
There is also this link to back my argument up.
You can disagree with it how much you want, you can throw a hissy fit, you can do whatever you feel like, nothing, will change the fact that cars become classics with age. And that age tends to move along as time goes by. One day, a 2017 Bugatti Chiron will be a classic.
Edit: And apparently, i know more than you do. Who refuse to accept that time keeps going on and things change.