Halo 6 will bring focus back to Master Chief says Frank O'Connor.

Halo 5: Guardians was a Halo title highly praised by its focused 4v4 Arena multiplayer, however, there was some fan backlash regarding the single-player aspect and how fans barely got to see the story unfold around Master Chief. In a recent interview with GamesTM (issue #186), Frank O’Connor, and Kiki Wolfkil acknowledged Halo 5’s campaign problems:

We very much realized that people wanted Master Chief’s story of Halo 5 (…) We definitely marketed in a way that we hoped was going to bring surprise, but for some fans and certainly fans of Master Chief, it was a huge disappointment because they wanted more Chief. It wasn’t that surprising to me, but the volume of ‘give us more Chief’ at the end of Halo 5 was significant and so I think if anything he’s slightly more important now than he has ever been, certainly to our franchise.

Frank continues to say the focus for the franchise will not be bringing new characters or expanding the number of playable characters. Instead, the studio will be “making the world a little bit more realistic and compelling and, I would say, more fun for players who get to inhabit the Chief in the future, pretty much as they demanded.”
This gives me hope Halo 6 is going to be solely about Master Chief throughout the campaign. Halo 5 took a similar path as Halo 2 with the introduction of Arbiter, and at the time most fans weren’t pleased with this change. E3 is around the corner. We know Halo is going to be at E3 in some sort of a story segment perhaps for Halo Wars 2 or a teaser for Halo 6.