First of all, La Légion is not a Special Force. Yes, they are some of the toughest men on the planet, which for some spend their life training and in operation fighting all over the world and are recognized among warriors for it. Still not a special force.
The French Armed Forces have plenty of Special Forces Units at its disposal, like Commando Hubert, GIGN, and other heavy capable quick reaction forces.
The French Foreign Legion has a very brutal training system. Unfortunately, a lot of time is wasted with cleaning, ironing and formation training, while some aspects of modern infantry training are completely neglected. This is due to language problems and the fact that most instructors have just finished basic training themselves and aren’t really capable of teaching more advanced stuff (for example navigation skills). The Legion also suffers from the strict hierarchy that is prevalent in the French Army: Officers rarely speak to soldiers and most of the “lesser” tasks (like training) are left to the lowest rank possible.
Discipline above all – To integrate people with different cultural and social background the Legion has a very strict discipline. “La mission est sacrée, tu l’exécutes jusqu’au bout et s’il le faut, en opérations, au péril de ta vie.”(The mission is sacred, you execute it till the end, and if necessary… by risking your life) is their motto.
The French Foreign Legion excels in small unit tactics. Due to the fact that in the beginning most of their soldiers don’t know French, the Legion has drilled their soldiers in the use of nonverbal communication on the battlefield. Legionnaires react very quickly, which is a big plus, especially when it comes to anti-ambush tactics.
However, the Légion got his own special unit, the GCP (Groupement Commando Parachutiste), which is a special force unit with personnel selected among the 2ème REP, an already elite parachutist regiment of the Légion. The best of the best in other words.
Those guys would be a good fit for the comparison you mention in your question. But, having the possibility to train and work with former legionnaires, it often surprised me how these guys could, often at the same time, excel at certain tasks and completely fail at others.