Specializing should be a little more creative than just leveling speed
If two people create the same character with the same attributes, but one person specializes bow, they will be the exactly the same until maybe 10-15 levels later a noticable difference in their bow level.
thats boring.
add more variety like access to different weapons, abilities or spells. then there would maybe be reason to specialize in skills like swim, trap, and cooking etc.