The principle problem is the following, the more diversity is allowed for player characters the harder it becomes for those characters to be integrated into the world.
With me moving from a class based system to GLoG and now to a classless system I am allowing my players to play more and more unconventionall “classes”.
While I am taking care not to have any classes at odds with the fiction of the world, I feel dynamics like your classic wizard looking for other wizards to either learn from or steal their books are becoming rare.
As long as Wizards are the only MUs it obviously makes sense for them to seek out each other.
But what buissness does a Pyromancer have talking to that Wizard NPC.
I dont magical abilities to be a rarity so simply creating a bunch of different magical NPCs wandering around isnt a solution to me either.
Mayber others more experienced with weirder PCs have advice on how still have world elements relevant to specificly that “class” of PC
Yeah I completely agree it’s a downside. One standard approach is the subclass thing, so pyromancers would exist as particular kind of magic users.
But yeah, I think it’s why for classes it’s usually helpful to start games with a very limited palette, although you can still do nonstandard options like pyromancer, barbarian, and assassin instead of fighter, thief, and wizard.
I think it kind of depends on the rest of the context of the game.
If anyone familiar with magic (or even anyone at all) can cast spells from scrolls, there is your reason to want to call on or steal from a wizard.
If anyone can learn magic eventually as a skill through downtime activities, there is your reason to seek out the wizard.
If characters need to seek out seniors of their discipline to advance, the pyromancer might not visit a wizard, but they’ll ask the GM were the nearest pyromancer NPC is located for the same effect.
Etc.
So without knowing the specifics of your table I find it hard to say if I relate to the difficulty you describe.
I never run into it, but I might run very different games from you.