Bolded is the important point here - the reason for the black screen in its entirety is to create a seamless transition from one point to another. It's a pretty game industry standard effect to mask extremely jarring movements over long distances, some developers simply have better ways to mask the transition with environmental tricks (Dark Souls does a whole bunch of these transition trickeries, for example). It's the same reason there's black screens when you go through things like portals in The Chrysalis, Halicarnassus in O3's desert maze, etc. The actual area you're warped to exists right next to the arena field you fight in and could theoretically get moved there without a load screen in 0.5s, but the movement is insanely jarring. Which is the ultimate point here why raise has the fade out - it creates a much more smoother, pleasant on the eye transition.
However, there is a crucial point that you get wrong about your shukuchi example - shukuchi is not an instantaneous movement, your character slides to the location quickly, on top of the camera follows you during the slide to match your character's movement. This is extremely important, as it creates the exact same seamless transition from one point to another that's pleasing to the eye. With raise being point A -> point B with absolutely zero interpolated locations inbetween, there is no opportunity to create the fluid motion from one location to another. That's also without factoring in that the theoretical highest distance for shukuchi is only 20yalms, whereas with raise you can get raised 30y away, creating an extremely jarring camera snap from point A to point B.
As far as potentially emulating rescue and causing the body to slide instead of warp? I doubt that's possible - we already know dead bodies can interact with stages elements (like if a diamond weapon platform gets destroyed, the dead body falls off of it and gets respawned elsewhere. I have zero doubts trying to slide the body over instead of warping it would cause the body to interact with field elements like pits/etc and cause a massive delay/issue in the respawning process.
For another example of why the developers do the fadeout - why do you think animation developers bother to animate the frames of the character moving in between one location and another, even when they're moving at high speeds? Or even during instant teleporting like in DBZ, why they always leave & create distortion effects at their start & end locations? Simply having a character start in one location and end in another is extremely uncanny for the vast majority. If you want an in-game example of something that looks extremely uncanny of instant warping, go do Elusive jump off a cliff with an area you can land on below. Your character will instantaneously snap to the bottom of the cliff, but the movement itself looks insanely wrong.
In the couple of gaming projects I've worked on at AAA studios, anytime we had instantaneous teleporting and hadn't put in the fading yet, the game testers would always complain & submit bug tickets regarding it citing that it looked wrong/broken - at the end of the day, it all comes down to the perception of smooth movement or the suspension of disbelief of moving from one spot to another without making it look uncanny.