Perfect Susanoo was originally Indra's avatar and therefore requires Indra's level of chakra, it's why DMS Kakashi was able to use it. Sasuke would need Sage chakra to achieve it and the one he used in war arc was a pre-mature version of it like full Kurama being an incomplete form of Ashura's avatar (the three heads),
I always believed Madara using PS without Sage chakra was because mastering Susanoo was his MS ability, him and Hashirama were blessed with monster chakras even for transmigrant standards. The way I see it Kishi did not give Madara any other MS ability in return for having the power to use the closest version of PS.
Sasuke had Indra's ninjutsu skill, Itachi had Indra's genjutsu skill and Madara had Indra's chakra prowess. Sasuke would not be able to unlock PS without Sage chakra hwever based on Oro's research he was eventually going to awaken Sage chakra even without Hagoromo's help. The question should be how long would it take for him to unlock Rinnegan ?