The "mythology" you allude to is older than western gunslinger stereotypes or western films per se, much older. He was nothing less than a prophet of God straight out of the Old Testament.
He was tasked, led and strengthened by God.
He was completely blind which makes his journey and it's success a miracle of God.
To infer that he was partially sighted would imply Eli could take some credit for his success at transporting the word of God and surviving.
Remember the book doesn't make it to Alcatraz but the word of God does.
God was solely responsible for the success.
This is punctuated by the fact that he is shot, left for dead only to be caught up to by Kunis' character walking on the road with no real hindrances.
It was a great story because the main character was God not Eli.
Eli was just a vessel that could be counted on to be "faithful".
He (God) totally confounds the "Wise" and the "Wicked" by using a blind man to do his will and gets the last laugh on Evil even when they think theyve won.
Great on so many levels for so many reasons.