As I said many times, Tsunade is severely underrated on the NB.
She is not top 10, however she is easily top 15.
In fact most of the Kage are severely underrated. Practically all of them are top 20, when some people put them in high 30's
And it's mostly due to flawed logic.
Skill, Experience, Knowledge >>>>>> A special ability.
Special abilities are extremely overrated by people on this base.
Perfect example is Amaterasu which should technically solo practically everyone. Yet it has never done any real damage to anyone besides 4th Raikage who was acting like an dumbass just running straight at Sasuke.
Another example is Rinnegan. It grants equal abilities to everyone, yet look at the massive difference between the three users.
Rinngan Obito had no real skill with rinnegan and his battle experience with it was negligible. He was not a real threat with it.
Nagato had a decent skill with the rinngean, he was capable of taking the entire Konoha, practically on his own, however he did not posses enough experience with it to fully understand it's weaknesses.
Madara on the other hand... His skill with Rinnegan is on another level, and he has more battle experience than any other character in NV. Experience and skill are underrated. Tsunade has both, and while she may lack variety in her arsenal of abilities she certainly makes up for it with he skill and experience.