Then you need to specify which Setting.
Any setting..?
All Settings.
Character classes should be a part of the world. Should shape it as a narrative conceit in the hands of the writer.
The word "Paladin" (or "Herald", now, I guess) should hold weight in the Mists of Ravenloft and also on Krynn. It should be a part of the narrative structures of Faerun and Athas. It shouldn't just "Exist to Exist". Is what I'm getting at. For the purpose of the setting, of -any- setting, a character class or race or other aspect should have a purpose.
Wizards should have schools and orders and towers and spells named after them and undergo insane rituals to steal the power of the Gods for themselves or act as sages for players to call on. Clerics should proselytize for their deities whether through word or through deed and in connection to the church or as a radical heretic against it. Warlocks should seek out secret knowledge or engage in the plans of their outlandish patrons, perhaps stealing names for a Fey Trickster or swapping babies with changelings. Fighters should be part of armies or renegade bands or washed up swordsmen with legendary histories or folk heroes. Rogues should be Pirates and Conmen, Manipulators and Puckish Rakes. And Sorcerers... should... um. Do...
Something. Something that isn't just "Well a Wizard could be in this role, but I could use a sorcerer for it, too". Something that sets them apart.
For my setting I'm making them Arcane Nobility. In another setting they might be the hands and eyes of various cabals of ancient magical entities working against each other. In Ravenloft they might represent Accursed people who wield terrible magics and often undergo physical transformations as their powers grow! On Krynn maybe Dragonblood Sorcerers are the puppets of Paladine and Takhisis. Or just children playing in the garden while a war brews beyond the fence, blithely unaware of how good they have it while the danger builds.
Maybe Storm Sorcerers are descendants of Titanic Elements in a setting and their powers bear deep respect upon the High Seas for fear of angering the Sorcerer's Parentage. Or maybe the Abberation-Blooded Psionic Sorcerer has to lay low when the Order of Monster-Hunters come calling to "Purge the Land" of the abberant plague.
-Something- to make them feel like they fit into the setting. Rather than existing only to exist.
And, again, I'm talking about narrative trappings for NPCs and such, to flesh out a given campaign world separate from a player's personal characterization.
I just think it sucks that Sorcerers are often left on the wayside in most settings. Rangers and Artificers, too. They "Exist to Exist" for most worlds, with no more binding to the world than the idea that they're "Out There" and "Doing Things".