The problem with dismissing Minaeve and Vivienne as misinformed is that if you are playing a Dalish Mage you don't get the opportunity to correct them. In fact, you seem to acknowledge it's a known practice even if not one you or your clan agrees with. You say things like, "My clan always found another way," or something.
And as just noted, Dalish from Bull's Chargers is another elf who left her clan because there were too many Mages. It's not clear in that case whether it was acrimonious. "My Keeper thought I should see the world a bit," could be a sarcastic reference to being exiled or a genuine reference to a sorrowful and hopefully temporary parting. But it's another piece of evidence that promotes the three mages per clan rule as new canon.
Which, yeah, I think definitely does contradict the spirit of previous lore regarding the Dalish. And in that it's a retcon and getting hung up on whether we can technically reconcile it with what came before is just semantics. I mean, retroactive continuity doesn't necessarily mean changing events, it also refers to changing our understanding of events. New ideas that cast new interpretations on old events. That's what this does.
I also think it's very clearly introduced in order to circumvent the "But why don't the Dalish need Templars?" question.
Which is a fair point and I think if they didn't want to present the Dalish as having a clearly superior solution they should either have written it differently from the start, or written a better retcon that didn't feel so clunky. The Genophage storyline in Mass Effect springs to mind as one where you find out more information in later games but it expands your previous understanding rather than making you feel like Bioware had suddenly invented a bunch of new stuff out of nowhere.
From a purely narrative perspective, if you're worldbuilding, and you end up introducing pretty shocking new information about a major faction, years into the fictional existence of the world, and about the biggest thematic conflict in that world - I think it's fair for readers to go, "Wait, what?"
Like, whether you think they shouldn't have made the Dalish look so innocent before or not, this information doesn't come across smoothly. It doesn't feel like you're learning something new that makes sense.
It breaks the fourth wall. It feels like something someone wrote in order to get themselves out of the corner they'd written themselves into. Because that's the only way it makes sense.
I mean, even the people who are in favour of this change seem to be working from a meta-game perspective of "the Dalish were too perfect," rather than an actual belief that it fits well into their established culture and attitudes? The only way we seem able to reconcile this is "Well, uh, different clans are super different?" which, let's face it, is functional but again - on a meta level - is basically acknowledging there is no way to make the two conflicting presentations fit and so looking for ways the world can accommodate that conflict.
Don't get me wrong, this was a great game on many levels. I just really thought this particular retcon was weak.