Quote from Odinwolfe;1211280:
Fighter is pretty strong single target (mostly) even with just skill ranks and an upgraded weapon.
And pretty useless in others.
Some do have noticeably faster growth, like magic if you're going to be a firebolt spammer, puppets, and fighter.
Others have rather slow growth, like range and gunner, but will outscale others most of the time.
There used to be a point where some skill sets were plain useless. Considering that no skill set is considered useless now, I'd say the skills are as balanced as they can be at the moment.