In the upper level attacks it gets the elusive Extrasensory, Psyshock & Psychic all of which are much more reliable than Psywave (for in-game use it is 100% useless because at level 60 it only reaches psychic's power at best and for level 50 battles it should never be used)
So UB Burst seemingly getting a signature move kind of makes me want all the UBs to get a signature move (cut doesn't count, kartana). Sadly probably not in the cards, considering Assembly was showcased with Iron Defense, but it'd be fun. Nihilego, if only for being the most relevant of the 7, should really have gotten one I feel? It's entire shtick is being a parasite and empowering others, but neither of these are really reflected. It gets the Guard/Power Split but those aren't quite what I was thinking. A unique variant of Swagger maybe.
Psywave doesn't work that way. It doesn't have a Base Power, but instead deals fixed damage ranging from 0.5 to 1.5 x the user's level. For example, at Level 50 it deals anywhere from 25 to 75 damage. It cannot be super effective or resisted, but Dark-Types are still immune to it. Basically, its a less reliable Night Shade/Seismic Toss.
I think the reason they brought it up is because it doesn't rely on high offenses to deal damage, but you're still right about it being pointless. Psywave is just plain awful.
On the UB front, it would be cool to see Nihilego get some crazy neurotoxin move. Going off of the Swagger variant idea, I could see it being a Swagger/Flatter hybrid, sharply raising both offenses. That would give Nihilego some serious utility alongside Tapu Lele or Own Tempo Mons in Doubles.
And finally, of course Cut counts! It sucks, but it counts. (Seriously though, Cut should have gotten a severe buff after losing its HM status, just like Defog eventually got.)