In addition to the other answer, before the patch, players who did not own last episode's artifact experienced this power bug, and the fix was to pick up the old artifact from Cayde and Ghost at the Pale Heart. Ownership of the current artifact didn't affect anything. On tuesday's update, this was fixed. Now players who don't own the current artifact (like you) are the ones experiencing the power mismatch. So the fix is to acquire this episode's artifact, which you can do so by starting the mission chain that begins with mission: Na-Veskirisk, on Europa.