Wow that's just pulling logic out of your ass now. So you disregard his illness when he was alive? That just proves his limit as a character. If we take out the flaws of every character, then everyone would be on a much higher level also. And no, he got backlash because he has poor stamina reserves and also don't forget that he drains chakra by using the MS and also gets blind from it. And I'm pretty sure Kishi would not kill him off for good without showing all of his jutsu, which is why he revived him in the first place.
Obito has better and more efficient control of his sharingan, without the backlashes. And Itachi winning fights in no time was only because each of those fights he used genjutsu, and that wouldn't work on Obito I'd wager. And him being so smart to win every situation is just fanboism. He is intelligent, but you forget that so is Obito, possibly more so seeing as though that he was able to fool all 5 countries and subordinates into his plan and is also a master at persuading people to his cause.