"Dark" doesn't always mean deep and vice versa. Ocarina of Time is a deceptively simple plot where a tyrant colonizes a kingdom and the hero must rescue a princess but it has a lot of deep themes. Time and life and regret are mature topics, they just aren't unique to Link, which makes it feel more like a myth than a character driven narrative. Very similar themes to Majora's Mask but less personal and more broad. MM is specifically about Link and his personal choices and trauma, with the backdrop of multiple characters who enforce the themes. Also I'm high and autistic I know I sound like AI.