Many in the Naruto fan community liken Itachi Uchiha to a god, and he is perhaps the most respected character in the fandom.
In fact, it would not be an exaggeration to say that Itachi has a separate fan base of his own. And it is pretty well-deserved. Not only was he a prodigy from the village, but he shouldered a huge and a rather tragic burden for the village, all because of his undying loyalty.
Above all, his unspoken love for his little brother, the way he tried to safeguard him, right until the moment of his death, and even beyond; was one of the most heartbreaking revelations of Naruto Shippuden.
However, Itachi's strength is also one of the major reasons why he has a massive popularity, and many fans believe he could take down many of the other antagonists of the series, if he wished to.
On that note, let's explore whether Sasuke would have won the fated battle against his elder brother if Itachi was not sick.
Could Sasuke have beaten a healthier version of Itachi in his prime?
As was later revealed, Itachi was already ridden with an incurable illness when he fought the final battle with Sasuke. Besides, his eyesight had already weakened due to excessive use of his Mangekyo Sharingan.
The fight a visual treat for the fans, although Itachi's death did come as a foreseeable yet shocking outcome. However, his illness played a big role in his death.
Now, could Itachi have killed Sasuke if he was not sick? The answer is yes. If Itachi had more strength left in him, he could have. In fact, he could have even killed Sasuke in his weakened state.
Although this sounds like an overstatement, it is not. Itachi possesses a vast repertoire of jutsu, and has the indestructible armor of Susano'o, not to forget the Totsuka Blade.
The only reason Sasuke won that battle is because Itachi planned on dying in that fight, for Sasuke's sake. As Obito later explained, it was a battle to awaken Sasuke's Mangekyo Sharingan.
Therefore, it might be safe to say that Itachi could have killed Sasuke at any point, had he any reason to.