Saru and Tilly have had major arcs in each season. Pike and Spock featured prominently in S2, as did Hugh Culber with his return arc. Georgiou has featured prominently, particularly this past season.
It's ok to not like Burnham, but to claim that the Discovery universe is entirely dedicated to her is disingenuous. She's the main character, but the focus on her isn't abnormal. If someone doesn't resonate with the character, it's going to feel more excessive. But, ultimately, it's really not.
Also, this isn't TNG with 28 episodes per season where you could do the obligatory character stuff with the minor cast members
- Worf and Alexander or Worf and Klingon culture
- Troi and her powers or Troi and her mother
- Beverly and .....whatever
- Q shows up again
There isn't time to tell an arc-based story with only 13 episodes and pause to give Lt. Bryce an entire episode where he is trying to get over not being able to see his mother again or something. It just doesn't work that way.