Fact: Togashi at first wanted to go assign a Seinen magazine (Weekly Young Jump) but Shounen Jump convinced him to stay with them. That's why HxH feels like a seinen at points.
I my opinion, Kurapika's arcs tend to be more mature because it's more grounded on realistic aspects of human life. Both his arcs involve corruption, political madness, conflicting interests and many negotiations; which lead to violence but also to a reasonable resolution of certain dilemmas (although something must be given away in compensation, it's never a perfectly humanist or liberal treaty). I like this, I like this portrayal of humanity even if it brings up an opressive atmosphere. Maybe that's why I love Kurapika so much, because he's caught up in very interesting and tense situations that make the series very amusing.
The succession arc was also very narrative-breaking in its regard as well. I didn't feel like it had a prevailing character, it was more of a bridge between two arcs. It had some elements of Kurapika's narrative, but it was heavily centred on negotiations, politics and institutions, which was very nice. In this arc, Togashi has succeeded in create a narrative-breaking point that doesn't rely on a specific character.