Itachi and Shisui's PS are nothing more than fanservice for the game. They aren't meaningful to the story at all, so yeah, in that sense, they are a "waste of time", I guess. *shrug*
There's nothing viably connecting their PS to the story. Shisui canonically died before he could even use the regular Susanoo, so his PS can't be canon. Itachi never used PS in the original story, either, nor did he imply that he ever could use it. It could be considered authentic that that's what their Perfect Susanoos would look like had they actually been awakened, but they were never actually awakened, so they aren't canon. They can't be treated like abilities they actually possess.
:wut: :wut: :wut:
Seriously...? What does that have to do with literally anything I was saying? Of course the original pilot manga isn't canon. Did my point not connect with you?
Original Naruto pilot (drawn by Kishi) = not a part of the official Naruto story ∴ not canon
Medieval fantasy Naruto cover (drawn by Kishi) = not a part of the official Naruto story ∴ not canon
Itachi and Shisui's Perfect Susanoos (drawn by Kishi) = not a part of the official Naruto story ∴ not canon