Honestly, this. I don't know why people have issues just accepting the fact that she is the strongest medical in the world currently. It's not like it means that it solos their fav or anything. Unless their fav is a fodder.
Because it's not stated anywhere in the manga that she actually "surpassed" Tsunade. She only 'succeeded' her when she 'retired', and even then, she only went on to become the 'lead doctor', in "KONOHA".
Last I checked, KONOHA does not equate to the world.
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People put Kabuto ahead of Sakura, because he actually has strong feats beyond medical ninjutsu, but are in the same category. Let's refer to the real world names of the things he is:
First and foremost, a doctor. He was the de-facto proxy to everything Orochimaru did, even during his fight against the other two Sannin. A doctor so good, he was helping out even his enemies in need (Chunin Exam, healing Hinata). He was an archeologist, digging up corpses of the long dead for their DNA. A Pathologist for the same purpose. An Anthropologist, discovering what Madara had hoped for, and giving him everything he desired, at a prime age. A Genealogist, Neorologist, whatnot. He was practically an all-in-one, and a master at everything, who wasn't given the credit he deserved.
Of course, Sakura is some is some of those things as well, and Naruto is even fewer, and their individual skill varies in different things.
I'd put Kabuto > Sakura > Fodder Medical Ninja > Naruto in being doctors. double the >s for my view on being scientists.
But then again, Naruto, in spite of not knowing how to explain, knew enough to pull off a full stem-cell transplantation, so that's the biggest medical ninjutsu feat in the manga for his credit.