It has always been the very best 80s Bande Dessinée to me and I have read it countless times, starting from my late teens. It is highly documented and still utterly poetic, philosophical and theatrical. It's simply better than most of Shakespeare's work. There, I've said it.
I would not dare read it in any other language than french however. Every word matters, every picture makes sense, usually at multiple levels of emotion or understanding.
You can endlessly re-read this serie, just mentally choosing who is the main character each time, and your perception of the world will change. And then you blend it all again and it's vertiginous.
Sorry, by documented, I mean that François Bourgeon did a lot of medieval and artistic research to produce those books (as always). But you are correct, his work is also analyzed by scholars and teachers, first among them is Michel Thiébaut with "Dans le sillage des sirènes".
We also have a similar wording "Le tout est plus que la somme de ses parties.". We usually attribute this saying to Aristotle (with some variations)