Ok, for starters, the magic appears to be for the most part, a wielded natural force for arcanists. So a minimum of invocations to external beings.
It is heritable and replicable, however, study of it is not a science yet, as wizards learn fixed forms of magic, barring a few spells. Therefore learned magic is a mimicry of innate forms of magic, requiring complicated factors to deliver effectively on the fly. Simply moving your fingers and saying the words isn't enough, the components must change to match the scenario and target.
Spellcasting process
Arcane
-Learned: Form the mental construct for the spell's shape, then by shaping the right symbols mentally, physically, and verbally, you call upon the fundamental concept of the spells and adjust the symbols relative to each other so as to fit the current place, time and target.
Then you release the construct and it draws the energy from the world to realize its effect. Each component can be reduced, but doing so converts its symbolic weight to a mental one. The greater the spellcaster's skill, the more the symbol reflects the origin of the magic, and thus the more potency.
-Innate: Your soul itself is the shape for the spell, and unlike the wizard, you don't need to adjust the shape to fit the world. You simply release your inner font of magic into the particular spell shape and with the raw power, release the spell-shape into the world. Imperfect spells(i.e. missing components) can be overcome by altering the shape and shoving more energy into it.
-Object: Magic items are basically a fixed spell matrix, charged with magical energy from its creator. Expendable items are basically battery powered, once the internal pool is depleted, it cannot be normally recharged. Limited use items draw energy in from the world steadily to recover their energy reserves over time. Permanent items are a whole complete spell matrix, which by their existence, continue to empower themselves, drawing from the world's ambient magic to replenish what little is expended.
-Borrowed Power: Clerics, Binders, Warlocks, Druids, using external power sources. Two forms are available, the less invasive being the prepared version. In this form, the supplicant requests the external power source with a supplication and is filled with the charged spell matrix as appropriate to their position and spiritual capacity. Casting it is simply a prayer request for the sponsor to complete the spell matrix.
The more invasive version fundamentally alters the supplicant's soul, much like the sorceror's, this lacks an innate font of power, so spellcasting is simply opening yourself to your sponsor, whose energy takes form through the imprint. The limitation is the capacity of the supplicant's soul, it can only conduct so much energy before it needs to recover it's own essence.
-Spell-like abilities: The "True" form of the magic, you don't mimic anything or channel any energy. You spiritually speaking, ARE the very thing the learned magi imitate to draw down power. It takes no effort, just bringing that aspect of the spell to the forefront.