I'm still making minor additions to the Lore post, so it's not done, just so you know. 

Two new ideas:

First of all: we're probably going to go with Trapezoid's weapon idea. In addition to the Raiment, you can choose to spend some of your crystals on a weapon as well(the nature of the weapon is entirely up to you). The more you spend on your weapon, the more powerful, but also the less you have to spend on your Raiment(which impacts your abilities). 

There's been an alternate skill tree form suggested to me, and here is my version of it:

Each class has some amount of basic skills, each one has element point requirements, and they are all the prerequisites to unlock more advanced skills in the same sort of vein. 

For instance, one branch of skills for the Knights could be terraforming techniques. The basic would be making a hole to try to trip your opponent. You could expand on it with a variety of things. A fissure instead of a hole, or put spikes in the hole. Each level you get to add one to your repertoire, but some will have element point requirements. So you could only advance so far in the terraforming skill tree if your Earth is low. 

This would make it slower gaining skills, and I would compensate by handing out levels more often. But it would make characters more specialized, and allow you to make your skill choices over time instead of basically deciding it all at once. 

Thoughts?