The three original books of Dungeons and Dragons, including Men & Magic were published in 1974. The first supplement, Greyhawk came out in 1975 and introduced a number of rules clarifications and additions, many of which would make it into Advanced Dungeons and Dragons a few years later. Among other things, tables were introduced for Strength, Intelligence and Constitution that provided explicit bonuses for high ability scores and explicit penalties for low ones. Here is the table for Strength:
The To Hit and Damage bonuses were only for fighters. Indeed, fighters with 18+ Strength could make a further roll with percentile dice for even greater bonuses:
Fighters of exceptional strength are now far more formidable opponents, and those of extraordinary strength even more terrible in that they can hit more easily, do more damage, lug large amounts of loot around without encumbrance, bend iron bars and perform other feats of strength with ease.
It's worth noting that the tables say nothing about how Strength might help one "bend iron bars". This would have to wait until the Advanced Dungeons and Dragons Player's Handbook was published three years later.
But I want to go back to my original question. Consider our friend Xylarthen with a Strength of 6. The new tables would seem to offer more reason why "there was no real chance for him to become a fighter." Now, in addition to his 10% penalty on earned experience, he will have a -1 penalty on To Hit rolls, may carry 50 fewer gold pieces and will be glaringly ineffective (50% worse than the average man) at bashing open heavy dungeon doors.
But at the risk of sounding like a broken record, I'm going to ask again, are those things so bad? Do the penalties significantly increase the chances that Xylarthen will, say, fail to make it to 2nd level? Is the character just "hopeless" in terms of mere survival? Or is there something else going on here?