I agree, killing off Cayde was not necessary for story development. A simple twist of the plot would have sufficed to have us chase a new breed of bad guys around. The bad decision of killing Cayde also killed off most of the games identity, it's humor, it's gritty feeling. Since Destiny 2 lacks any personality, I suppose this was an easy fix for a lack of a centralized purpose or storyline distinct from Destiny 1. But now as we see, we are back feeding off Destiny 1 1) cause its cheaper and 2) Destiny 2 has no real story of its own.