"That is correct. Even on my own star, the amount of aether present within any living being varies, and there is no guarantee that every being will be capable of harnessing that aether to any meaningful degree."

Some can, certainly. But not all of them, by a long shot. Admittedly the fact that most creatures are something that has been deliberately created does play a role in that but that's normal enough to Lahabrea that he doesn't see any particular reason to mention it.

"The basic requirements are the same. All spells require concentration and aether. More involved ones may either require longer periods of focus, or have specific gestures that are necessary to call the invocation into being. Some may require both."