Samurai Double Dot?

[Rongway]

Not that it makes it any better.... but anatman, hyoton, and physick on summoner have been useless abilities pretty much the entire time they've existed too. They likely intentionally made kaeshi higanbana not apply a second dot, and just make it an incredibly niche ability (like when you're in fights with two bosses. Hansel & Gretel as well as Xun-Zi & Meng-Zi both in Tower at Paradigm's Breach are examples of this)

Being a niche skill isn't the same as being a skill you never use.

If you need to DoT two enemies for some reason you'll do more dps if you use regular Higanbana twice rather than lose a Kaeshi:Setsugekka. If you used Kaeshi:Higanbana on a second target, it would only discount you a single Sen, which you could have built up manually in two hits. Kaeshi:Setsugekka is worth three Sen, which would have taken eight hits to build up.

Kaeshi:Higanbana is a bad niche ability that people should never use.