The way I see it, James Gunn has two main thematic modes: gleeful nihilist, and sappy idealist. It might seem like an odd pairing to some, but these two facets go together so well that they frequently blur into each other–like peanut butter and jelly. For the full James Gunn experience, you need them both.
But while the Guardians of the Galaxy movies have all the sappiness, their darker side isn’t really all that dark. Vol. 3 definitely moved the needle in the right direction on that imbalance with Rocket’s newly revealed backstory and some of the High Evolutionary’s other atrocities.