To sum it up, I believe all (or most) skills should have a proper scaling, based on stats, to prevent them from becoming less useful the more you advance.
Right now, only a few skills scale of stats and the majority keeps the same damage they had when you advanced classes before, so they end up dealing proportionally less damage to monsters as you go leveling up.
Therefore, instead of using a diverse combination of skills, which it seems to be what the game wants to promote, you just use the latest skills you got since they deal better damage, and the rest eventually end up on the background.
It also makes sense that the majority of swordman and archer skills should be based on their attack damage (probably STR for swordman and DEX for archers), not just on the skill level. I always found it funny, as an archer, to have Oblique Shot deal substantially different damage than my basic attacks, independently of the bow I’m using (while the skill is simply a normal attack which bounces).
And of course, the wiser the wizard/cleric, the stronger the magic (or so it should be).
With scaling, skills from low ranks could actually be on par (number-wise) with skills from higher ranks. Since I suppose you aren’t picking that class for a skill with high numbers, right? You are picking a class so you can do cool things with, to do some combos using skills from classes you got before, and create an unique character.
The class system in this game is so amazing, but I believe the lack of skill scaling is quite a hidrance to it.