Why give literacy to the main hero if he is stronger than everyone else, and there isn't even a hero in the army who could learn these spells? In my opinion, it's a waste of free skill slots.
In the fifth game, they did a good job re-editing many skills from the third part, and the separation into skills and abilities is a great idea.
Of course, giving literacy to the main hero doesn't make much sense, but using this skill with other heroes in a scenario or campaign still provides some benefits. Examples of using this secondary skill were discussed above...
And also: can we please stop talking about the 5th game for a while?