I don't see why I shouldn't consider what lead to her confession if you overlook it and fail to mention it.
Yes Naruto had realized that years ago. Sakura never exactly hide that.
But the confession wasn't exactly to get Naruto to marry her and live happily ever after- she was on a suicidal mission and she was trying to negate the importance of promise before she went. If she succeeded even then seeing how Japanese stories of that kind go and how much 'nod' Kishi gives to Japanese cultural sensitivities, they wouldn't end up together. It only would render the promise pointless.
Besides that Sakura too didn't know that Naruto had made a promise to Itachi too. Sai basically told them she didn't understand the full impact of her ancient request and rest of Konoha 11 basically pushed her in corner. How would Naruto react if Sakura went after Sasuke and died(or killed Sasuke) without meeting Naruto? How about he feel about his promise to her and how Konoha 11 pushed her in to killing Sasuke without taking him in confidence?
Was there any good scenario here?
That's really just an assumption and totally based on personal whim. If we are going to do that there are other considerations. e.g.- In most Japanese/Asian stories when one of the guys ends up dead by the hand of a friend in a triangle the other two spend their lives as bachelors. And Kishi is known for keeping things cliche. So we will never know.
I am calling a spade, a spade. Not being written well is not good enough excuse to exaggerate the problems and make it a punching bag to get over personal issues.