The curve is a script note
A steep drop in the first 30 seconds means the title promised something the opening did not start. A slow bleed means the video is longer than the idea. Spikes mean people replayed a moment. Those spikes are your shorts.
Chapters help if they are honest. They also give restless people a way to skip, which is better than them leaving the video entirely. Satisfaction, not just watch time, is what you feel in comments: did they get the thing you promised?