How authentic are constructed languages

Pedigree edhellen? Elvish, Dothraki and Klingon: How “Real” are Constructed Languages?

"In any case, I believe that Esperanto shouldn't have any native speakers." <- Yes, there are (in the meantime) also native speakers of Esperanto.
See e.g. (also for further literature)

Esperanto is what is sometimes also called a world auxiliary language in literature. At the end of the 19th century there was a kind of movement that dealt with this issue. Esperanto is not the only language of its kind either, less popular, but perhaps halfway known, is Volapük. As far as I can see, the Esperanto movement was partly connected with the labor movement of the same time.

Languages ​​like Quenya, Na'vi or Valyrian, on the other hand, tend to serve artistic purposes, as opposed to an "humanity is better off when everyone speaks a common language" idea.

In this respect, I would contradict: These are two different things.

In the English-speaking world, planned languages ​​are called Conlang. Sometimes there is a distinction between "Auxlang" (auxiliary language) "Artlang" (artistic language in the sense of the word) and "Engelang" (engineered language; languages ​​that are quasi experiments, e.g. Loglan or Toki Pona). differentiated. Esperanto would then be an auxlang, the languages ​​from film and television would be Artlangs.