It's not Bear McCreary if you are reading this prior to the Beta launch. In Beta 1, the plan is to reveal Bear's Soundtrack for Ashes of Creation at that time.
Who composed the music in the Ashes of Creation videos and livesteams?
Maybe you have discussed the Fireball animation in the Alpha One Preview of the Mage Archetype | Levels 1-10 Active Skills video? The music in that is the song "Epic Sail" by Immersive Music.
Other songs by Immersive Music that you may be familiar with:
You can legally use Immersive Music from premiumbeat.com You can purchase a standard license
with unlimited web based projects for $49.
There are more songs and composers.
One of my early favorites after discovering Ashes was Ashes of Creation - Merry Christmas! back in Dec 22, 2016