I think that the majority of people feel that way, Gasai needed more screen time, there was so much I wanted to know about his past, how the legion would be when Gasai finished taking control.
On your other point of the conflicting themes,
I don't really see why they're bad, to me it makes it feel more realistic. Someone's life can't just be full of dark, melancholy themes like revenge, justice, etc,etc, there has to be a balance.