Chaosmancer
Legend
You are making a lot of campaign specific assumptions about spell casters here.
There is a lot of room for interpretation about warlocks in particular.
“In your study of occult lore, you have unearthed eldritch invocations, fragments of forbidden knowledge that imbue you with an abiding magical ability.”
“Your arcane research and the magic bestowed on you by your patron have given you facility with spells.”
There is also text about adventuring etc.
My only point here is that no where is it suggested warlocks are passively getting powerful: tutored and rewarded? Sure. But you can make a good case that they are actively pursuing knowledge.
You can also see that they adventure.
I don’t get the feeling that shiftless lackwits get 5, 10 or 15 levels of power—-just like that—-that the local rat catcher is suddenly formidable as a rule (without risk and adventuring).
In short: I don’t think this means spellcasters of high level are common. Nor that those that exist just happen due to patron whim. Maybe a low level one can happen like that but no ability likely means no advancement.
How common is a high charisma? I suppose you could get to high level with a 10….that would quite the feat! And once there your charm or command would not knock all of your foes down…
So if magic use is “common” in your world that does not presuppose that powerful magic users are. Think about the he local militia guy vs. the 10th level battlmaster. The former is common but does not mean the latter would be.
I'm not making nearly the number of assumptions you think.
Anyone can get magic by making a pact. This is true. Maybe you make a pact to be taught magic and it takes you time after the pact to learn any magic, but the Hexblade's patron is a weapon, and the GOO patron may not know you exist. Additionally, level 1 and 2 are explicitly apprentice levels. Basic beginning point for a class is supposed to be level 3. So, level 5 is just an experienced member of the class.
And I'm not going beyond 5 in most of my examples. The local military guys are about as good as a level 1 fighter, and I don't care about the level 10 battlemaster. I'm looking for the level 5 character. Which if we just use extra attack as our measure, is not that uncommon. They are uncommon, it isn't like every guard is a 5th level fighter. But it isn't like a 5th level fighter is some figure of legend who only serves as the greatest champion of the king either. It wouldn't be that uncommon for a captain of the guard to be a 5th level fighter, for example.
These are assumptions, but they aren't major ones. And since I'm not talking about 10th or 15th level characters, we don't need to worry as much about the rarity. 3rd to 5th level characters would be uncommon, but not unheard of.