You are right, Sasuke is stronger. But only about 6/10 times he would win.
Sasuke:
Ninjutsu: high s rank
Taijutsu: high a rank
Genjutsu: low s rank
Intelligence: high a rank
Strength: high a rank
Speed: high s rank
Stamina: high a rank
Hand seals: low s rank
Itachi
Ninjutsu: high s rank
Taijutsu: low s rank
Genjutsu: high s rank
Intelligence: high s rank
Strength: low a rank
Speed: high s rank
Stamina: low b rank
Hand seals: high s rank
Ninjutsu: Tie
Taijutsu: Itachi
Genjutsu: Itachi
Intelligence: Itachi
Strength: Sasuke
Speed: tie
Stamina: Sasuke
Hand seals: Itachi
Itachi wins 4/8, Sasuke 2/8, tie 2/8
But we have to take some consideration to account.
Ninjutsu: Despite them being equal, Sasuke has more variety of an arsenal. Here are the main ninjutsu they can use.
Sasuke's top 3:
Amaterasu/blaze relase
Kirin
Susanoo
Itachi:
Amaterasu
Susanoo
And Since Sasuke has ems susanoo (not perfect) and Itachi has ms with legendary weapons, they are equal.
Blaze release pawns amaterasu anyday, seeing how Sasuke is better at amaterasu anyway.
Push comes to shove, Sasuke can use kirin.
Taijutsu: Itachi may be better at taijutsu, but Sasuke is physically faster and has more stamina/chakra. They are the same speed. So Sasuke probably wins, even though it won't be easy. And Itachi has a pretty good chance also.
Genjutsu: is basically counted out, because Sasuke and Itachi can easily break out of Tsukyomi and it would be a pointless genjutsu war from then on. And Itachi would be winning yes, but would run out of chakra before Sasuke.
Intelligence: Sasuke is a genius too. But Itachi pawns him here.
Stamina/Chakra: This is the main thing that makes Sasuke win. Sasuke almost has half the chakra of Itachi+His own. Sasuke will win in the end because of this, probably.
Hand seals: Itachi wins this, but a lot of Sasuke's jutsus don't use hand seals anyway.
In the end, the only two things Sasuke really has to worry about is Izanami and Itachi's intelligence.
But, Itachi has to be cut two times to do it. And Sasuke with chidori katana might kill him before Izanami.
But yet again, Sasuke wins most likely with high diff. Itachi may win with extreme diff though.