Cant you see how important that is?
If you really think that Hancock wont play any role in the future,you're deluded.For example, I could logically theorize that Hancock has used up all of her importance in One Piece. Is she still important to Amazon.com" onclick="re_hook(71)" target="_blank" href="http://www.amazon.com/gp/redirect.html?ie=UTF8&location=http%3A%2F%2Fwww.amazon.com%2F&tag=msmanga-20&linkCode=ur2&camp=1789&creative=9325">Amazon Lilly and the Kuja pirates as their strongest warrior and leader? Sure. Does she have more to contribute to the ongoing narrative? Probably not.
She has been one of the most held back Shichibukai in the war and we have yet to see her in a serious battle,not to mention her feelings towards Luffy.She's gonna play some role in the future for sure.
And Hancock doesnt affect the OP world near as much as Marco does.
Firstly,Marco being on the same level as the admirals,someone who according to the Gorousei was the only one together with the emperors,who could stop the advance of the BB crew.
He's one of the top strongest people in the world and he's the most likely candidate for the next leader of the Wb crew.You cant possibly compare someone like him to Hancock.