I thought Sasuke's 'source' of senjutsu was Jūgo - hence how he was able to cover his Susanoo in that swiggly curse mark... sh*t.
Whatever.
I'm sure he'll land a hit (now) - with Naruto's help. Before? Maybe, maybe not. His taijutsu isn't exactly stunning and it's average at best against another sharingan user, nevermind
Madara Uchiha who has experience on his side
My friend argues
"... but he held his own against Itachi!..."

Naruto held his own against Itachi - in taijutsu -
in his Nine-Tails Chakra Mode. Itachi could (should) have wiped the floor with Sasuke, if he hadn't been y'know... dying and intending for Sasuke to kill him.
Point: Sasuke's Taijutsu is sh*t. Taijutsu is needed to damage Madara - Might Guy leading the charge on that one, Sasuke cannot (pre-SotSP) outdo Might Guy and his 8 Gates.
Sasuke has speed on his side in Shippuden against the likes of Naruto & fodder. But against Madara? Pfft. He needs the Rinnegan to equal his eye prowess.
He needed a boost in power as Madara has several (Wood Release, Hashirama Senjutsu, Ten-Tails).
Sasuke now has a -one- Rinnegan. EMS. Senjutsu, via Jūgo. Power-up from SotSP. And Naruto.
He has a chance
now - he didn't before. Madara was toying with him, well...pretty much everyone, but Sasuke was no exception.
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