I didn't mean to imply that passive traits and filler traits were synonyms Phazonfreak. I think if a passive bonus exists as a full level-up option, then it must have noticeable gameplay effects. If you play any modern RPGs, this tends to be the rule. For instance, in Skyrim, a passive bonus may be healing spells +50%, +20% weapon damage, +20% armor protection, certain spells cost 50% less (any of these might work here too). Each time you use these things, the gameplay effect is noticeable. Diablo 3 is an over the top example, for 50-60 levels each level-up is a new active/passive effect or a gameplay (often visual too) change to an existing effect, and often a combination of both.
Here is the first impression one gets to the leveling system for each class to make the point:
Level 3 assassin. You have already chosen your class, that comes with a set bonus and opens a tree, cool. Level-up again, you have two choices, +5 accuracy or +4 dodge. It is very hard to discern the gameplay effect of these changes, but you have to take one to even get started. Level 3 choices here are barriers, of themselves almost microscopic in effect.
Level 3 for the defender tree has +10 defense when not doing anything and +20 magic resistance. I think it is hard to be impressed with either. Spells are actually kind of rare to target a specific unit, and an unpredictable chance to defend against them (an extra 0% to a high % depending on the caster) is not the first thing you are worrying about starting out as a melee unit. Regarding the +defense while defending, it will only come in to effect if you don't do anything the first turn of battle or have a quicker opponent, unless you are just passing to try to soak up damage. I know the tactic of passing to be a damage wall might be effective, but it is hard to be excited about being a battle turtle (and not the teenage mutant kind!).
Level 3 for the commander is +5 accuracy for the army or -10 unrest in a city. If you are thinking of putting a level 3 hero in a city for unrest reduction, that hero is a dud. The other I guess is supposed to just add up over time, but you won't feel like level 3 made any difference for the accuracy of your army.
Level 3 for the warrior is +3 attack or +10 hitpoints. Definitely the most noticeable of all classes. It makes a difference the player notices right away. (Though +3 attack fades in usefulness over time, maybe why %weapon attack or damage might be a better way, heroes use their weapons better)
Level 3 for the mage is +10 spell mastery or +1(2?) levels to summons. The spell mastery bonus is tricky, you will never know if a spell went through because of it or not. It is just not very exciting for your very first level, and more is on the way. The other path is strange, unless you are a summoner sovereign you don't even have summons yet! This level makes either no difference or a difficult to discern difference, and it is the first choice you get in the trait tree.
Later on many branches bog down in to sequences of passive bonuses, which all together over a series of levels add up to something that is noticeable, but individually it is hard to tell the difference from level to level. +Accuracy is hard to notice in doses, +dodge has the downside that you will never know when a miss was because of the bonus, +attack to champions when you hardly ever face champions, small bonuses to army stats, +3 defense... most of the passive bonuses are too small to be noticed in and of themselves. So each level-up is not an increase in power, it is a step toward an increase in power. That takes away from the thrill of seeing the level-up screen.
*edit: I think Skyrim has a great model for passive trait bonuses for warrior classes (interesting model for mages too, but that is quite different). In abstract, the best bonuses are available right away (+%), are in the root of the tree and they are repeatable after certain requirements, which would be equivalent to levels in this game. All traits are meant to be immediately used and noticed, and most are never outdated. There is almost never a point you are taking a trait to get to another trait. The effect of this system is leveling up is always exciting, and the game sells an 8 digit number of copies (other factors contribute to this too, but just sayin).