I'm the parent. You seem to mistake population level effects to single person events. For a reduction of a few years in a global population, a bunch of those people will be walking around and suddenly drop of heart failure and die 30 years earlier than they would. You should look up additional papers on this subject to get a better idea than a single random metastudy. There's plenty available on the effects.

I'm not saying if everyone sleeps 1 less hour a night they will all die 40 years earlier, but if you start sleeping 4-6 hours a night consistently you will have problems, and if you're unlucky you might have an accute heart issue that may take your life. There's no reason to play with sleep in extreme ways.

On average not wearing a seat belt reduces global life expectancy a certain amount. But for the guy laying on the tarmac spit out of the windshield it takes 40y of his life.