No obligation to behave the same way, yet you're claiming they specifically wanted to gut both of them and that Aether will be nerfed to behave the same way as Soaring Slash on a suicide kill. You're claiming the two of them were targeted for sharing a unique trait of killing the victim first, which I pointed out was untrue due to Climhazzard and Axe Kick's behavior. You're claiming it made more sense to set out with a specific goal of making both moves kill the user first, see that one of them did not kill the user first after easily succeeding with the other move, and then just leave it that way for the time being instead of adjusting Aether's descent to similarly kill Ike first.
It's possible you're right and they have a vendetta against these moves. It's possible Climhazzard, Axe Kick, and Aether will all receive additional changes to neuter this mechanic across the board. But you can't tell me they wanted Aether and Soaring Slash to behave the same way, and then tell me they don't have to behave the same way. For now, evidence points to them wanting to address the Chrombo and how the two moves possessed such immense knockback they would meteor all the way to the blast zone from the top of the screen.
Edit: Now what does give me pause about this, is that apparently according to Beefy Smash Doods Chrom may also be able to sometimes die second if he catches the opponent from low enough. I would expect the opponents and height it works on are even stricter than on Ike's, but we'll have to see if they keep changing them or leave them alone from now on.