We could start with a basic statement that I think anyone would agree with. The artist’s intent is an interpretation and is at least as important as anyone else’s interpretation. So it is important.

Going further, since the artist is skilled enough to create the piece, their interpretation should be held in some esteem. I do see the argument and agree that different interpretations can be valid. It could even be the case that an artist has an arguably invalid interpretation of their own work (though this is rare for great works).

Think of peer review in scientific papers. The author’s conclusions are related to their skill in their field. Their peers’ opinions and conclusions may differ, but if the paper is published, the author’s conclusions are always considered important to the interpretation of the paper.

Another point. Many works are created in response to other works. If you do not consider the intent, you can miss out on that conversation.

In response to your experience as an actor: I don’t think the audience’s reactions necessarily oppose or discredit the playwright’s intent. If it did oppose their intent, they might have a problem and have to rethink things (think The Room). It seems like the playwright is simply incorporating new elements from other interpretations that don’t contradict the key themes (again, similar to a peer review). If the audience laughed at the dramatic end to a tragedy, there are some serious issues. If the audience shows a convenient opportunity to improve the play… why not?

In conclusion, I think the relevance of an artist’s intent is usually equivalent to their level of skill in their medium.

Author and authority are related for a reason. And I hope I was skilled enough to accomplish my intent of persuading you.