That it's well developed, and one of the best in TWD-verse.
But it is, from the perspective of Morgan's story and development. We understand Morgan's motives, we understand what Nick represents (Nick is Morgan to Morgan's Eastman). We understand why Morgan is reluctant to be in the role of Eastman. That conflict is established, followed through, and given pay-off.
Point A: Morgan maintains emotional distance from everyone to avoid dealing with loss and death.
Point B: Morgan meets Nick.
Point C: Nick, a troubled character, having recently experience some sort of trauma (the nature of which is not yet clear to the viewer) and is seeking vengeance for it, tries to open up to Morgan and get some sort of guidance.
Point D: Morgan refuses to become to Nick what Eastman was to him.
Point E: Nick gets his opportunity for revenge.
Point F: Morgan cautions Nick against seeking revenge, due to the unintended consequences of violence, but due to Morgan's emotional distance, Nick does not take his words to heart.
Point G: Nick kills the Vulture and gets his revenge.
Point H: Morgan, realizing the err of his ways and seeing Nick in himself returns to accept his role as Nick's Eastman.
Point I: Morgan lets down his barriers and breaks through to Nick, much as Eastman broke through to Morgan.
Point J: Morgan did so too late and Nick's violent act of revenge, as Morgan predicted, simply resulted in the circle of violence continuing and Nick being killed by someone else seeking revenge.
Point K (presumably, if this story is followed through on): Morgan realizes that inaction (specifically, his inaction) can lead to violent and unintended results, just as revenge can.
Point L: Morgan grows as a character due to this realization and begins to form meaningful bonds again (with the remaining Clarks, Al, and Dorie).
Like I said, you don't have to find the story to be an effective one. But there is no denying that, in terms of Walking Dead storylines, this one has themes that are clearer than most and has a more natural progression than most. The actions of the characters and conflict between them is consistent with what we know about the characters and develops in a linear and rational manner. Its not like Walking Dead Prime where Daryl trusts Dwight, then doesn't for no greater reason than because the plot necessitates Tara forgiving Dwight and someone else doubting him to generate artificial conflict or Jesus switching from pacifist to "I am part of a conspiracy to kill Negan" simply because Maggie needs people on her side and he is the best positioned to be on her side.