Rest kills at around 55% It is not that early for a move that is really risky and hard to land. And most players know how to DI.
Um, then why are you pushing for earlier kills rather than pushing for better Rest options and setups. Earlier kills in a two-stock game like Smash 4 is absurd to begin with -- even Melee Puff didn't have this sort of dynamic where it's either you get KOs really early, die really early or nothing happens; one of Jiggs main passive pressures is the threat of Rest, and that is pervasive throughout her entire gameplan. By giving her more options to Rest from, that pressure extends into these options. You don't just want to avoid some hard read and raw Rest, you want to avoid getting jab reset, avoid getting upthrowed and a bad DI follow, avoid getting into a position for easy tech chases, and so on. Killing earlier and earlier isn't what Rest is about, it's about an extremely fast, early kill option
relative to the rest of the cast that is hard to land and has high risk on whiff. The very natural extension is for options to minimize the possibility of whiffs.
Look at Gimr with 9s all day, how that extends throughout his gameplan, how others feel about it and how it's set up. It's a comparable scenario; the main differences are that 9s are RNG, it's slower, it has a larger hitbox that's disjointed, and G&W has setups. It's already in a healthy place
because there are setups.
The disadvantage of Star KOs also has nothing to do with getting a win in the last few seconds, either. What are you expecting, a Rest offstage into Star KO where you die first?