Once Sasuke masters his EMS, he will without be stronger than Itachi, as he likely will have access to Perfect Susano.
Also, i dont know if you are talking about them fighting each other or other opponents but here is my two cents.
Sasuke is a bad match up for Itachi as Sasuke's Sharingan is strong enough to be able to overcome Itachi's genjutsu which are fatal to others.
If Current Sasuke was to fight Itachi, it would be really close but id give it to Itachi because he is overall better than Sasuke.
Itachi is smarter than Sasuke
Itachi's movement speed is faster than Sasuke, but above all, Itachi's hand movement speed outclasses Sasuke really bad
Itachi's Taijutsu and weapon plays are better.
Their physical strength are the same.
The only real argument in Sasuke's favor is actually not really in his favor.
People claim that Itachi's stamina is very low and all, some believe it is due to his illness and some say he is just born that way. I try to put that damn databook aside and look at how Itachi fought when he was dying from the illness he had while fighting Sasuke.
When it comes to that, Itachi's stamina seems to be just as good as Sasuke's.
Itachi used roughly 6/7 Mangekyo techniques worth of chakra;
Tsukuyomi which was fired back at him
Amaterasu
Amaterasu
Stopped Amaterasu's flames
Popped Susano
Popped it again with complete form to fight Oro
Transfered Amaterasu to Sasuke
Sasuke pretty much did the same thing against Raikage and Mizukage until Zetzu had to feed him chakra, the only major difference is that his Susano was clearly not complete and he himself talked how the pain he was feeling was likely nothing compared to Itachi's.
If we list what they did and if we take in consideration the fact that Itachi's Susano was perfected and that on top of it all, he was going to die anyways from his illnesss... i'd say that damn Databook stat doesnt tell me much.
So instead of going back to part 1 and claim that Itachi's stamina is clearly low because he ran away after 1 Amaterasu, how about u go further into the manga where he used 6/7 Mangekyo techniques worth of chakra on top of being dying ill and holding back to an extent.
We also have to remember something of great importance, Chakra effciency is a big factor.
Ebisu's lesson on chakra efficiency showed us in part 1 that Sasuke wasnt really good with using his chakra, and was using more than he needed thus was wasting some.
Itachi is the best genjutsu user there is how there, and to be good with genjutsu, you need high intellectual capacities as well as a very good chakra control as the job is the control someone's chakra with ur own. With that said, Itachi is likely one of the best when it comes to chakra efficiency which could explain why even tho Sasuke has more chakra, he doesnt seem to have more numbers when it comes to actualy fighting.
So to sum it up,
Current Sasuke vs Itachi ; i still give it to Itachi, even tho his genjutsu will be rendered useless, Itachi is better overall and also has Toksuya and Yata's mirror to protect himself.
Once Sasuke fully perfects his EMS / Susano, he will have surpassed his brother at long last, he just hasnt yet.
And when it comes to them fighting again other Shinobies, Itachi is the most versatile and dangerous of the two because now his genjutsu is not countered like it was with Sasuke.
Sasuke is able to use genjutsu too but Itachi's genjutsu outclasses him obviously, thus giving Itachi an even bigger advantage over Sasuke.
But again, once Sasuke perfects his EMS, he will always be on top due to Perfect Susano (What i assume will come with EMS)
As for the Kabuto fight... stop trying to troll Sasuke or Itachi.... they were holding back the whole time, and Itachi was leading the fight so Sasuke was ''forced'' to watch Itachi do the whole thing because Itachi wanted to do so.
Sasuke did save Itachi but thats because Itachi saved him in the first place and him doing so put him in a vulnerable position (Spikes from the ground / ceilling) Had it not been for Itachi's efficient chakra control, he wouldnt have been to keep Susano up to protect Sasuke.
And Itachi would have never gotten chopped in half if it wasnt for him casting Izanami on Kabuto for his sake, as if he had wanted to kill Kabuto, he wouldnt have wasted his time trying to put him in a illusion that would eventually put him on the right path he has been seeking his whole life.