Mate. He was able to kill Danzo and strong characters, but also got destroyed by characters that weren't so tough.
dude danzo is the worst example of sasuke being strong. That fight was setup for a victory from the start and it was meant as nothing more than to A) kill danzo off and B) give more backstory to itachi having killed the uchiha. what so many people fail to realize is that danzos izanagi as all izanagi, work on reality itself, meaning that not only sasuke but obito could have done nothing to see through it, so why did danzo continue to die, alter reality so he was still alive but continue talking for the rest of the episode when he could have just respawned and stabbed sasuke or slit his throat? because kishi never intended there to be any chance of victory. Now as for why he has been getting roughed up. gaara has become far more powerful (not necessarily chakra wise) since they fought in series one, back then he was going at half strength trying to contain his emotions and not using hardly any of the one tails' chakra. Killer bee stomped him simply because he was a beastly son of a gun, you cant expect sasuke to waltz into any battle and make a fool of anyone he fights, that would make it far too boring. And lastly i think kishi is allowing it to happen because he may finally start bringing some decent character developement to sasuke, and i mean actual struggle to attain power. Up until now, he has pretty much been handed his power. Sharingan makes grouth in taijutsu and ninjutsu, as well as genjutsu effortless so he never had problems with those. He attained ms by beating naruto, sure he worked hard for that but at the time naruto was still pretty much a joke compared to his current state, his only big attack was rasengan and dont forget sasuke had the curse mark drastically powering him up too. Then he finally got ems, once again, sure he beat itachi but it's still pretty safe to assume itachi was going at 95% tops since he was glad sasuke beat him, not to mention he was very sick so it can be argued he was probably actually fighting at around 70%~ of his healthy max. Did he scrape through to beat those two? yes, but that doesn't beat the fact that while he narrowly beat them, kishi still wrote in minor details that made it clear he would be victor (naruto not wanting to kill his friend, and having virtually no skills just heart, itachi being sick and quite almost wanting sasuke to win and kill him).