In at least the first through third editions of Stormbringer the rules really do indicate that unless the GM says otherwise a PC's nationality is randomly rolled, and this absolutely could result in one PC being a Melnibonéan sorcerer and another PC being a Nadsokor beggar. (This potential disparity between PCs is mentioned in examinations of the game here and here.)
…But is this flawed?
By contemporary standards, this may seem deeply flawed. However, many of gaming's earliest experiments—and Stormbringer is certainly among those, its 3rd edition (1987) largely unchanged from its 1st (1981)—weren't particularly concerned with balancing the PCs against each other.
For example, Villains & Vigilantes (1979) and Traveller (1977) both use, in part or in whole, random character generation that can lead to one PC being significantly more powerful than another. In V&V, this involves rolling which superpowers a PC receives. Like its TV Tropes entry says
The "official" way to roll up a character for the game was to pick a table of powers (like general powers, magic/psionic powers, magic/psionic items, and skills), and then roll percentile dice to determine what powers your character had. This could result in some strange combinations, which can also be seen in some of the characters, like Mace from Crisis at Crusader Citadel [and here]. As his name implies he wields a tricked out mace, but for some reason also has a superhuman sense of smell despite having a background that fails to suggest he's anything more than an everyday thug.
(Link added.) A particular V&V example is the superpower Heightened Endurance that can add 3d10 to a PC's Endurance score. Assuming a starting score of 11 (on a scale of 3 to 18), a lucky 3d10 roll sees a PC with an Endurance score of 40, and a massive increase in the PC's hit points. A typical PC without heightened ability scores has between 3 and 12 hit points; a PC with Heightened Endurance could have well over 100! Similarly, in classic Traveller (a character generator for which can be found here), a PC could have sufficient starting funds to skip adventuring altogether and go straight to retirement, maybe giving the title of his spaceship to the less fortunate PCs before he departs for a life of leisure.
Even Advanced Dungeons & Dragons is no stranger to this: Its Player's Handbook (1978) includes the so-totally-optional psionics rules. Determining if a PC had psionics is a bit of a trial:
Characters with one or more unmodified intelligence, wisdom or charisma
ability scores of 16 or higher might have psionic ability. Whether or not this ability is possessed is then determined by a dice roll using percentile dice. Any score of 00 (100%) indicates the ability exists. For each 1 point of intelligence above 16 add 2½% to the dice roll, for each 1 point of wisdom above 16 add 1½% to the dice roll, and for each 1 point of charisma above
16 add ½% to the dice roll (drop all fractions). (110)
Then if a lucky PC possesses psionics, the player rolls to determine his PC's number of attack modes, defense modes, and minor and major disciplines. Then the player rolls again to determine which minor and major disciplines his PC possesses. In the end, a fortunate level 1 illusionist PC could end up able to employ the equivalent of a 9th-level spell, while an unlucky level 1 fighter PC could end up being a fighter.
My point is this: Stormbringer is far from unique in having mechanics that may yield a PC who is significantly more or less powerful in the abstract than another PC. And,—both because I am no apologist for this process and because I lived through this era while being infamous in my circle for my utter lack of dice luck—, I can say decisively that Yes, this kind of sucks. However, ultimately,—the theory goes—it shouldn't matter if PCs are not balanced against each other. Let me explain.
It's potentially unbalanced, but it's also fair
So long as no one's using loaded dice or bribing the GM to get special treatment or whatever, creating a character randomly is completely fair: every player has the same chance to have an awesome PC. While it seems wrong that you are playing a scurvy-ridden penniless Nadsokor beggar while she is playing a noble Melnibonean who can summon the gods of chaos, you and she could've just as easily rolled differently, and your PC would've been the sorcerer and hers the beggar… or you could've been both sorcerers or both beggars!
Once PCs hit the table, though, a role-playing game of this sort especially is cooperative, and it's cooperative on a much larger scale than the character sheet in front of the player may indicate. A player isn't bringing only his or her character to the party. A player is bringing to the party a whole 'nother brain that adds to the group a further layer of experience and knowledge. Also, the player's bringing to the table—in the form of his PC—a whole 'nother set of actions that couldn't be taken were the PC absent. Those—let's face it—priceless additions to the gaming group are present no matter how terrible the PC! It's up to the player to put his own brain and his PC's actions to good use no matter how execrable the PC.
Also, keep in mind that the real challenge isn't even on your side of the screen. Your PC is randomly generated: you had no choice! Had the GM wanted PCs balanced against each other, he wouldn't've had players make them randomly! That makes it the GM's responsibility to build a campaign that involves equally all the PCs no matter how absurdly different. Your responsibility as a player is to trust that the GM is doing precisely that and to use your knowledge, experience, actions, and character sheet to play your PC to the best of your ability even if that character sheet alone sucks.
That's one of the great appeals of random character generation: being able to tell stories afterward about how your awful, worthless PC survived and thrived to become the Vagrant Monarch of Nadsokor… or how, after failing his first pick pockets roll, he died to one blow of a city guardsman's club.
Note: While further examples abound, my favorite OSR version of random character generation is The Mutant Epoch (2012)—a sort of super-advanced Gamma World (circa 1983's 2nd edition) that pulls no punches in its random character generation—expect the crazy. Similarly, no discussion of unbalanced PCs can be had without mentioning Rifts as it is famous for ignoring the idea balancing PCs against each other, this interview with the game's creator even explaining why. A Rifts party can consist of Dr. Strange, Professor X, Smaug, and a hobo with a shotgun and a pocket full of candy. However, by contrast, Rifts typically leaves it to the players to make unbalanced choices rather than having entirely characters generated randomly. (Also see this question and this question.)