I think this mission and its place in the campaign is a major part of the games pacing problems.
Up until this point I was pretty okay with Lockes missions, I felt like a mystery was in front of me and that that journey would end with the Chief finding Cortana. Instead we meet her half way through the game. At this point I kind of want answers and the game doesn’t provide them. Maintaining that mystery until the end of the game would have been good.
The mission also ends with Cortana about to let them into the Domain. This butchered the Sanghelios sections for me as I immediately felt like I was playing catch up and that the story had effectively stopped. This murdered the tension and sense of build up as I knew things can’t progress until Chief enters the Domain.
Personally I would have put Reunion after Sunaion but before Genesis. This way they maintain the mystery and things naturally escalate from finding Cortana, meeting Exuberance and then entering the Domain. With the mystery they under way less obligation to explain Cortana’s actions in Halo 5 as she only appears near the end. I would also have much more enjoyed the elite missions in my first playthrough. I literally ended Meridian wanting to go to Sanghelios and ended Reunion wanting it to end as soon as possible. That takes some doing to a massive Arbiter fanboy.
I suspect they did this because they didn’t want people to go too long without Chief but it’s not like we didn’t notice. It’s a very poor decision. Also they can play around with things like the timeline.