Another question: Albus is level 9 and Sion is level 8. But their class levels are 10 Swordmaster and 6 elementalist respectively. Can anyone account for how that system works?
Each character has a character level and a class level. A character level determines your stats, equipment you can use, and the amount of available TP. If you play in challenge mode, the game will add additional levels to enemies if you overleveled the mission. Treat it like usual levels you have in RPG.
The class level opens up masteries and abilities. Masteries are opened at lvls 1, 4, 8, 12, and 16. Some masteries can only be obtained by leveling a certain class for a certain character. Also class level opens up abilities (like double slash, wind wail, lightning bolt etc). You have a limited number of ability slots, so you should choose which ones you will use.
Once you will reach character level 15 and class level 10, you can transition to advanced class. I recommend to train basic class up to lvl 16, to open up all abilities and masteries of the basic class. Each character has two advanced classes. Let's say it is class A and B. Each advanced class opens new abilities and masteries. Class A can use abilities from Class A, Class B, and basic class. But, class A cannot use masteries from class B. Only from class A, basic class, common, and human ones.
It may sound complicated. This is because it is complicated) But, there will be more complicated stuff later in the game). My advice would be to level basic class to max level, and then level to max level both advanced classes. After that you should figure out how this part of the game works.