The proverb refers to the notion that anyone with an advantage over a group of others is likely to thrive. The explanation is in the proverb - if everyone is blind, the man with even one eye has an advanatge over everyone else, and becomes the king. It is used to imply that even a slight advantage is just that - an advantage.
I always thought it meant the leader is the person with the best credentials in the group but that doesn't necessarily make them a good leader. The one eyed man still has only one eye.
True, he does only have one eye, but as the proverb points out, he is the one with sight in a kingdom of blind people, so i reiterate, even a slight advantage is ... an advantage.
However, someone with 2 eyes would have better vision. Everything is relative. In a kI'm not saying you're wrong, maybe you're right that the original meaning was your one. I'm just saying it could be interpreted differently.
I'm with Stoogmeister - I have always thought this to be a disparaging term along the lines of if compared to all the idiots you're not as idiotic as them...but you're still an idiot