I heartily support this. My partner is in medical school. It’s kinda amazing how much knowledge he is learning and how much he had beforehand to be able to absorb as much as he does now.
His aptitude tests were in the top 10% of applicants (not of the population.. of applicants for medical school) and he only got into 1 of his 4 choices of medical school because standards were so high. (The good news is it does only take one though)
I think being a doctor is a good equivalent for being a spellcaster that learns their craft rather than it coming from some natural spark. I.e it’s bloody hard work!
And there's a simple answer for those that don't learn it as a craft--namely, Sorcerers and Warlocks, since all the others
do require training. It's pretty easy to address the gap. E.g. Sorcerers, as already noted, are unreliable at best--many people who have draconic ancestry (or the like) don't know it because it's several generations back, and all the intervening generations in living memory didn't manifest any powers (common origin story is suddenly
finding out you have Sorcerer abilities.) That depicts both the unreliability of such powers, and the degree to which they sort of "appear" and have to be managed. Simply put, it's the reason why mutants haven't taken over the world in X-Men: the X-gene is rare, it activates in weird ways and for weird reasons (genetics is super complicated like that), and it's a roll of the dice exactly what happens and why.
Warlocks are, of course, a bit trickier, but there are two ready-to-hand explanations. First, it is simply not true that just anyone can become a Warlock: you need to find some way to establish the connection to a patron
first, and
then you can make a deal. This is, as above, a pretty common baseline concept, that the Warlock gains their power not from rigorous study per se, but from delving into forbidden libraries and stealing dark grimoires, or breaching sealed temples to forgotten gods, or performing a devil-summoning ritual, etc. Like how
eldritch power spending bills are legally required to
start in the US House of Representatives and then go to the Senate. There are procedural tricks to massage that requirement, but ultimately in at least a formal sense, the process has to start in the House and then pass to the Senate. Warlock pacts appear to work the same way in most cases: it's not that patrons are constantly broadcasting job opportunities to the aether and any Joe Shmoe can show up for a perfunctory five-minute interview. You already have to have done some legwork to make a pact happen, or at least
someone has to have done that work. Second...patrons, just like deities, have every reason to be picky about who they give their powers to. You don't want to bet on a lame horse, if you get my meaning.
Those answers--again, well-supported by most presentations of the class flavor and abilities--pretty well knock Sorcerer and Warlock out of the running for "and thus every social climber is going to be a spellcaster in basically every world." Certainly,
some will be. Power corrupts, after all. But these examples are gonna be really
sporadic, and keeping the secret of the warlock pact is gonna be hard if you find any way to pass it down the generations. Secrets don't keep forever--especially when you're technically displaying the secret in broad daylight, and just hoping people don't figure it out.
This directly relates to the "instability" stuff I spoke of in an earlier post. Sure, due to the vagaries of life, you'll almost certainly eventually run into a spellcaster with the lowercase-c charisma, narcissism, and skill to try to take over a region, but without the delusions of grandeur that lead to trying to become the Dark Lord of Everything and thus getting ganked by a plucky band of heroes. The problem becomes, their power won't
outlive them unless they can either achieve immortality (which, uh...has a really bad track record in terms of avoiding the aforementioned Dark Lord tendencies) or ensure their offspring share their talents. Those classes which avoid the need for long training are also the ones least likely to be easily preserved across generations without issue; those which are easiest to preserve and transmit to offspring are also the ones most likely to detract from learning the skills and forming the connections necessary to rule effectively.
Again: that doesn't mean this is impossible. Magocracies will probably form. But, in a lot of cases, they'll either be unstable, or naturally shift toward an oligarchic kind of government where a
council of mages will call the shots. This, as noted, is at
perilous risk of oppressing non-magic-using members of society, and not even purely by intent. A world where every person is expected to be able to
purify food and drink is a world where you don't
have Poison Control Centers. I definitely think that intentional oppression is going to be the much bigger concern most of the time, purely based on what minimal things people have used to justify slavery and other horrors IRL, but unintentional stuff like that is going to be a real problem too.
