There are even the ones he couldn't use, like [Light Bringer], [Life Return], and [The World]. Ancient Power is unlike ordinary skill that Angus could master after a few times trying or practicing. Ancient Power is a kind of conceptual power.
The power itself is similar to supernatural powers that break the law and physics. It will only become more potent as the user comprehends its concept. Basically, the more the user uses it, the stronger the power.
However, since this power originated from Angus and Jayna, they need to know what kind of concept and intent from the original creator before being able to master it. The Ancient King who created the Ancient Power has their own understanding of it.
Other users will never be able to fully use it even with the blessing of the Ancient King unless they have the same understanding and experience as the Ancient King.