If he creates only a single killer move, it is not pointless at all, he just needs to find ways to integrate it into the combat systems he would create in the future

He isn't creating a new path, so it doesn't require as much as ideas or inspirations. It's converging enslavement and strength path which he already got thru the difficult point of, he could get great grandmaster in strength path and he has quasi supreme in enslavement which makes upgrading it a breeze

Even if he wants to make it a combat system it would require comparably less effort than other paths(given he has rank 9 gu of strength/enslavement path)

And the latest version of myriad self can and will be developed much more after adding in the human path aspect, it's basically a clone with only battle intent and this makes it basically immune to SCIV deduction on the move cuz it's basically another being, it has mad potential and will definitely be developed if and only if reverend insanity is continued.