The general choices - except for the Potential line - are fairly good. You get something for each pick that will make a difference - initiative, attack, hit points, the ability to equip four accessories.

Potential is a problem because of the nature of what it is. Taking all three gives +60% experience. The problem isn't that these are filler, but that they are so good that not taking them in some ways makes your champions weaker in a longer game. A trait that boosts XP is not very exciting, however, and by taking it you're deferring picking cooler traits for the sake of hopefully gaining traits faster. I wonder if this would be better off with only one or two traits instead of three - or replaced with something else.

An example of what I mean by filler choices is:

Endurance I (10 hp) -> Chain Mail Proficiency -> Brute (+3 attack vs. lower level) -> Enmity (+25% attack vs. opponents of opposite race) -> Plate Mail Proficiency

This tree is three different things. Endurance gives you more hit points, brute and enmity boost your attack power conditionally, and chain and plate proficiency give you the ability to wear armor. I can't see any clear theme that links these traits together as a group. 

I kind of wonder if Brute and Enmity would work better as general picks, and the chain could be Endurance -> Chain -> Plate, meaning that to wear plate, a warrior champion wouldn't have to invest five picks. Three picks is still a decent amount, but it gives you more freedom to pick things that may work better with your playstyle, like the bonuses to particular weapons and/or maneuvers. I am not really addressing the branching traits from this tree at the moment because I mostly want to get the basic idea across.

There are some cool abilities in the warrior tree, but it seems that access to those can get deferred for the sake of being able to wear better armor or get more xp.

I wanted this to be a more comprehensive thing covering all the trees but I am currently in too much pain to properly focus. 

I think there are also issues with mages, specifically in that I find that I don't use them for much once I cast a few spells, and I have to choose between high initiative weapons so I can cast a defensive buff or a fireball or something early on, or low initiative ranged weapons if I want to do something other than cast a few spells and then let the rest of the units finish the battle. It also seems that some spells have a longer cast time than is really warranted by their effects - there's a fire spell that has a cast time of two that damages every unit on the battlefield. Compare to Dirge of Ceresa, which has no casting time, although deals its damage over time. I am not saying the fire spell (flame wave) needs to be instant, but that the cast time of 2 seems a bit high for the damage dealt, as compared to Dirge of Ceresa.

There's another issue in that ranged weapons for champions have the same effect on initiative for champions as they do for regular units. Of course, regular units can have up to six members, each firing its own bow, crossbow, or staff. The initiative reduction seems balanced in this regard because otherwise ranged units would probably be dominant in ways that make melee pointless. With champions, however, they're getting the same penalty, but only dealing a fraction of the damage. I am not sure what to suggest with this, and it is an issue that doesn't seem to be as big of a problem with melee weapons - possibly due to the smaller initiative hit (or no initiative hit) for melee weapons.