The boot speed wont increase because the drivers are not loaded at every boot. They are just saved on the drive and if the hardware that requires those is connected, then the drivers starts. Like the already enabled drivers in libreelec.
As far as i know libreelec is preconfigured kodi OS. There is just kodibuntu(outdated, dead?), openelec(dead?) and libreelec. I dont know of any other "regular linux distribution" that starts directly into kodi where you dont have to setup complex things. I cant make "any distribution start up with Kodi after booting".