Dalish Clans Can Only Have 3 Mages
Another explanation for the “Dalish clans can only have 3 mages” — other than it being another piece of chantry propaganda to make the elves look bad/justify their own mistreatment of mages — is that this is a lie Dalish tell non-Dalish to keep the Templars off their back, bc you know that if the Chantry heard that Dalish clans have 10+ mages they’d be lighting that shit up big time.
Alternatively, it’s half true in that they have 3 official mages — the Keeper and their First and Second in line — and everyone else is just another dude who happens to have magic. Case in point: when you side with the werewolves against Zathrian’s clan, a bunch of randos start coming at you with magic. There’s no reason you can’t have magic and contribute to your clan without being a wizard all the time.
In regards to Minaeve’s clan, we already know that the Dalish are not homogenous. It’s perfectly likely that for some reason or another, they’re just like that. Maybe they got attacked by Templars recently and decided to overcorrect in response, maybe something got lost in translation and they thought every clan was doing that now, or maybe they’re just assholes and don’t care what the other clans are doing. Just bc Minaeve’s clan is like that doesn’t mean the rest of the Dalish are the same.
Furthermore, maybe that’s where the misinformation comes from in the first place? One Dalish clan kicks out their mages, who end up as apostates or taken in by the Circles, and bc they’re the only Dalish mage representation most non-Dalish ever meet, they end up heavily misinformed about common Dalish practices. When talking to Minaeve as Lavellan, you can sound pretty surprised that it’s even a thing, like you’d never heard of it before bc it’s not commonly done.