I think so too as well. Magical proficiency is the related to how well one understands magical concepts and how well one is capable of manipulating the Veil and the energies of the Fade (unless if it is blight magic or blood magic). This has no relevance on someone's capacity to learn, read, write, and speak.
Its one of the things that I think exists due to D&D influence where mages are supposed to be the "intelligent" class and therefore the other class usually gets shafted when it comes to being educated or knowledgeable unless they themselves learn some form of magic. For example, a Rogue in D&D only really needs to invest in Intelligence if they want to be an Arcane Trickster (learn some spells) and a Fighter only really needs to invest in Intelligence if they want to be an Eldritch Knight (again, learn some spells). I can understand this from game balance perspective but I find it lame that spellcasting = intelligence.
To be fair, this has SOME historical basis.
D&D is basically a Medieval European fantasy setting, and in real-life Medieval Europe society was (ideally) divided into three sections: those who fight (the nobility), those who pray (the clergy), and those who labor (the peasantry). In Medieval European society only the clergy were consistenly educated and literate; they alone dedicated their lives to learning how to read and write and record historical and religious documents, while the rest of society did physical labor of some kind. (Working the land for peasants, working with goods for merchants, creating goods for artisans or craftsmen, fighting and hunting for the nobility, etc.)
This was sort of extended for the D&D setting. The "intelligent" classes are the ones who have their physical needs met and thus can afford to sit hunkered up in a dark room reading texts and tomes all day (not to mention writing tomes, books, and scrolls, which was all hand-written before the invention of the printing press, which was dang time-consuming). If you're a peasant who has to work the land all day or a fighter who has to train in combat all hours of the day to win against real opponents, you don't have the time to sit pouring over documents all the time. There simply aren't enough hours in the day.
Plus, like you said, gameplay balance. (Although I am glad newer games from newer IP are starting to do away with this, like with Pillars of Eternity, where different classes can be educated, and/or there are different kinds of education that work for different classes.)
However, as for the Dalish...
I can't believe we didn't catch onto this sooner. It seems so obvious now with Solas' revelations but you are right. In Dalish clans, some Elves are more equal than others though the disparity is not that obvious unlike, say Tevinter where if you are a non-mage, you are pretty much screwed.
Except the Dalish never claimed they were all 100% equal or all had 100% equal say in decision-making. Each clan is a group, each group needs a leader, and their Keepers are the leaders. All things considered, if they have to elect a leader, at least they choose based on knowledge and cultural memory (the elves were once immortal and magical, and they revere magic as a dying part of their culture, so they choose someone in touch with a part of their dying culture and who can ideally teach and guide based on knowledge and wisdom) instead of, say, the one who can hit things the hardest. (*cough*Andrastianhumansociety*cough*real-worldfeudalsocieties*cough*)
Also, there's no such thing as a perfect society where everyone is 100% equal. That's a myth that's been pursued many times throughout history and always crashed and burned. (There's a reason Sir Thomas More named his ideal society "Utopia," which is Greek for "not" or "place," meaning "no place," as in he knew such a place couldn't exist.) It's just not possible in group dynamics--not everyone is gonna agree or get alone or share the burden of decision making. Where there's a group, there has to be a leader.
I mean, Andrastian human nations are all monarchies, yet I don't see you accusing them of tyranny like Tevinter and Ancient Elvenan.
Honestly though, if you think about it, rogues and warriors are a lot more vital to a society because mages do not hunt for food or domesticate animals for food or grow plants or maintain social order (even in Tevinter justice is relegated to the non-magical Templars).
You could say the same about people who work with their hands in real-life. The peasants of feudal societies, modern-day farmers and mechanics and janitors and other blue collar works who do most of the physical labor of keeping our society up and running, yet tend to get the lowest pay and least amount of respect, and who don't tend to make as much pay as white collar workers / those who work with their "minds" (doctors, lawyers, Congressmen, etc).
But that's not human nature. Generally speaking, the people who do the physical labor are rarely the ones throughout history who lead in society, whereas the ones who have access to the most education and the "softer" lifestyle (as in not doing back-breaking labor for a living) were the ones who led and continue to lead. It's not right, but that's usually how it is.
In short, it's not just the elves or Tevinter.
I would not be surprised to learn in future games that Elven nobility bred the way like Tevinter nobility did. After all, according to Solas, Tevinter is built on the remnants of his people and we now known that by his people he means the Ancient Elves. Isn't it really ironic that the spiritual successor to Ancient Elvhenan, the ones who are carrying their actual traditions, are not the Dalish Elves or the City Elves, but Tevinter Imperium ?
Is it any different from Andrastian nobility believing they have "noble blood," and choosing to breed with only other nobles to keep their "noble bloodlines" pure? (When in reality most nobles got their stuff from their ancestors being the most savage warlords who managed to kill/drive away other warlords and then force the common folk to pay them to live on "their" lands, then work the land to produce food, and then give the noble family the lion's share of their crops despite the noble family doing none of the work?) Which conveniently keeps all the wealth, lands, prestige, and stuff in the hands of the noble families and out of the hands of the common "riff-raff"?
It's not just Tevinter or Ancient Elvhenan. That's just humanoid nature. Those in power will always find a way to justify it by saying whatever inborn ability they have that the masses don't makes them "special" and deserving of ruling (having noble blood for feudal lords, being magically gifted for mage societies), and they're gonna jealously guard those traits to keep the power in the hands of their elite families and out of the hands of the riff-raff.
Some even speculate that the Tevinter Altus class has purposefully interbred with elves in order to increase magical potential in their offspring. Hard to say... But since elf-blooded look just like humans, it's possible.
I'm in that party.
Elves = slaves but had great inborn magical power + Tevinter = the ones with power who coveted more inborn magical power + elf/human relations = human offspring. I refuse to believe for a moment that ancient Tevinter didn't find a way to put elven magical blood into their own bloodstreams but keep power out of the hands of elven mage slaves with so convenient a set-up. (Unless specifically told otherwise by the devs.)