I thought creating your character meant choosing what you want to do with that character. How does choosing your class at creation cause you to loose control of your character?
The farmboy who has to fight things and later discovers his magical abilities is a very common fantasy trope that D&D should support.
Other kinds of changes in character focus are also very common in the literature and IMO best represented in the game using multi-classing. Examples include joining a monastery, wowing to never use magic again, finding a swordplay teacher, a thief joining a more reputable organisation (magical or otherwise), etc.