New Ranked Questline (The Journey Begins)

Apparently the new ranked questline (The Journey Begins) which gives bonus XP, only counts in 5s; is this a bug?

IMO it should count in 3s because a) It's also ranked; b) Some of us prefer 3s to 5s. I'm tired of everything being geared toward 5s and 3s getting left completely out of the loop.