Exponential Experience and Proficiencies,

Since gaining levels is somewhat exponential and proficiencies gaining is linear I am thinking of making acquiring proficiencies more in line of gain xp rather then level. For example Fighters would gain one class proficiency at first, third, fifth, seventh, ninth, then one per level. Thieves would gain them at first, fourth, seventh, tenth, and then each level, Casters would gain one at first, sixth, tenth and fourteenth.

My thought is that really only the caster proficiency are powerful and it lets high level non casters have more specialization options. It would also allow high level “norms” to gain more leadership type proficiencies, allow high level characters to be more leader types an high level casters to be more magical researchers.

Would this seriously unbalance things?

be careful about your assumptions. XP requirements are exponential, yes, but so is XP gained. Take a look at the monster XP progression table and you’ll see it comes pretty close to evening out. The reason for the difference is so that characters taking on challenges above/below their level will have their leveling speed adjusted appropriately.