Isn't Burnham supposed to be the first officer?

[cultcross]

People were assuming that Burnham was going to be the Discovery's XO based solely on the fact that we knew she was the XO of the Shenzou.

This. Burnham was the first officer, just not for long. Combined with Georgiou's line about getting her own command that was in the trailer, people assumed she would be Discovery's first officer as some sort of proving ground and rise to command for season 2. It seems they're going quite a different direction.