Except the coefficient is oceans apart. Imagine if Fell Cleave hit every enemy nearby for the same potency as it does to its current only target. Would you assume that is balanced?
No? Because it does almost 3x the damage of the AoE?
Then why would you assume that (getting n times your single-target [not your AoE] healing potency per target) is balanced for Bloodwhetting?
Yes, Bloodwhetting is not unique in scaling flatly per target, since Abyssal Drain does the same, but there's that difference again: Abyssal Drain totals 200 potency of healing per enemy, while Bloodwhetting totals to 1600 potency of healing per enemy. And Abyssal Drain is a 1-minute CD, while Bloodwhetting is just a 25-second CD.
200. Versus 1600. 60-second CD. Versus a 25s CD.
Now consider what Bloodwhetting would look like if its AoE scaling functioned more like attacks, wherein total potency dealt does not increase linearly because you have to sacrifice potency per target in order to scale further:
Rather than 1600|3200|4800|6400|8000 total healing over 1|2|3|4|5 targets, you'd instead be doing ~1600|2000|2400|2800|3200, resulting in a curve that can actually be simultaneously appropriate both for ST and AoE.
Nascent Flash did not require a partner for most of Shadowbringers.
Nascent Flash no longer being usable on self came only after they wasted the second button by making Nascent Flash identical to Raw Intuition / Bloodwhetting (instead of having a pure mitigation tool (Raw Intuition) usable on self and distinct and separate healing-from-damage-dealt tool that can be used on self or others).
...And why are you dismissing people for "talking like a ShB player" when they're noting things as far back as Stormblood, let alone while you can't remember the content of the previous expansion...?