I read a rant about having to shift all my stuff to the "JAMStack", because what i'm doing is old fashioned or something, but I don't see how that will shave 73

I read a rant about having to shift all my stuff to the "JAMStack", because what i'm doing is old fashioned or something, but I don't see how that will shave 73% off my load time. I also don't see how a static site generator is good for most of my sites, seeing that they extremely dynamic applications. Also, the site talking about big pages being bad is pretty big.