You are ignoring the context of the conversation to get around the fact that you are simply angry that Vivienne spoke over your character (oh the horror) and wasn't respectful enough about the Dalish for your liking.
You seem to be taking the dislike of Vivienne very personally. If you can't handle me pointing out how Vivienne blatantly ignores the elven Inquisitor correcting her generalization of an entire ethnic group, then you're welcome to opt out of this conversation.
As far as I am aware we have never heard of a clan that has more than a handful of mages just because every clan does it differently does not mean that they do not take steps to protect themselves from the dangers of magic and one of those steps ls limiting the amount of mages in the clan. Most if not all clans seem to do this, Aneirin is a very special case because he was on the run from the templars, had already been trained by the circle and doesn't actually seem to permanently live with the clan.
We don't know what most clans do since no one addresses what most of the People do.
So the PC's point about the way the Dalish handle it is an incredibly bad one seeing as the Inquisition just opened it's doors to hundreds of mages and already had quite a few mages. Even with the few mages they have the Dalish take steps to protect themselves, this is what she was saying.
By citing an example that's only applicable to some clans, and not all of them?
Maybe Bioware could have given us a chance to present a better argument but that argument was in no way a valid one.
It's valid for the Inquisitor to say that the Dalish don't have templars; they certainly didn't when the Dales existed as a free elven state.
Why is the PC's experiences of the Dalish and more valid than Minaeve's? Where you really "correcting" her or where you providing an alternative experience?
It's more valid than Vivienne's generalization of the entirety of the Dalish.