Originally Posted by Lightbringer
Presumably so; however it currently appears not to have dawned on Sasuke that stabilizing Susanoo is a necessity to bolster it to its next stage. This can be due to a number of things, but I think its because of not completely mastering the douryoku of the Eternal—leading him to discern which methods would bring about the desired aesthetics. I think the ability to use the technique is there, but due to a lack of experience he has not realized it.
I'm merely claiming that it is because of the conjoining powers that create the Eien no Mangekyō Sharingan, that the True Susano'o is able to be birth in the first place.