So you really think Itachi the guy who has been talking about how the clan limited themselves and didn't test the limits of their capacity and they guy who has been talking about exceeding the limits of his capacity wasn't improving himself all this time.

That just plain doesn't make sense, sure Sasuke may have gotten closer to Itachi's level but since the very beginning Itachi has been waiting and preparing for this day even more so than Sasuke. Not to mention that Itachi has been in Akatsuki all this time so even if he wasn't training just being with those kind of people would force him to improve himself.

Since you mention that Oro said that Sasuke was better than he was when he was that age, I think its important to mention that Itachi defeated Oro oh about TEN years ago. I'm all for Sasuke and his deep-seated hatred but this doesn't make any sense at all, Kishi said that Sharingan can't beat MS, Itachi said so himself and now Sasuke is breaking out of tsukiyomi. Whats the point of killing your best friend to gain MS if your little brother is going to defeat it using normal sharingan.

Yes I get it Sasuke's eyes are supposed to be stronger than Itachi's they been saying that since the beginning and hate is supposed to be the source of the Uchiha's power and no one has more hate than Sasuke but MS>Sharingan. The only reasonable explanation I can think of is that Itachi's MS has gotten much weaker due to overuse but they never said you get weaker they said you go blind in exchange for power so even that doesn't make sense.

That is the only explanation I can think of though so I would say Itachi's eyes have gotten weaker and using the curse seal Sasuke was able to generate more power than Itachi expected.