I always found it odd that in France, maybe not all the time, many ordinary actors are referred to as 'comedians' or 'un grand comédien'. I was just watching an Arte documentary (on youtube actually) about Michel Piccoli and it described him as:
Portrait captivant d'un comédien hors norme.
Now he's really the last person you'd think of as especially a 'comedian'. In any case Truffaut in his Radioscopie interview seemed to me unwilling to accept the word as a general definition, so I think he must have saw it as a poor or outmoded description. It explains why Romy Schneider was totally perplexed when the interviewer kept on about it considering the tone and subject matter of the films they were discussing.
However, this is Alain Delon in an interview with Figaro in 2018:
Ma carrière n’a rien à voir avec le métier de comédien. Comédien, c’est une vocation. C’est la différence essentielle – et il n’y a rien de péjoratif ici – entre Belmondo et Delon. Je suis un acteur, Jean-Paul est un comédien. Un comédien joue, il passe des années à apprendre, alors que l’acteur vit. Moi, j’ai toujours vécu mes rôles. Je n’ai jamais joué. Un acteur est un accident. Je suis un accident. Ma vie est un accident. Ma carrière est un accident.
So his view is that a 'comedian' is a specialist who learns to only 'play' the roles, like an impersonator, whereas the actor 'lives' the roles. I don't think this is really as defined as that these days. Many comedians have put in exemplary 'straight' acting performances (think of Coluche in Claude Berri's
Tchao Pantin.) And Michel Piccoli is primarily known as a 'straight' actor in this sense. Straight actors sometimes do comedy. We know that, it's part of acting.
The words acteur/comédien are so commonly used as rough synonyms, but it still seems to me wrong to use it to mean any actor. Comedian has a defined sense and the original Greek, even if it might not map exactly to the modern sense of comedian, doesn't just mean 'actor'. If you describe someone known as a dramatic actor as a 'comedian' it seems weird to me.