Hardware creates limitations that even the most streamlined and efficient software cannot overcome. Even if you stripped an OS to its bare essentials for quick boot time, eventually you will have start other programs or processes when the need arises. Starting everything on the front end is the most expedient way to boot a computer.
A hard drive is extremely old technology, and even though you can get faster hard drives, there is a limit on how much information can be accessed based on the technology. Its like a Cessna versus a P51 mustang. Both use prop driven technology, but despite the P51 being faster, it cannot achieve speeds that a newer technology offers (a jet engine).
