Don't try to compare Tsunade's taijutsu with Kakashi's. She's more skilled in taijutsu (IMO) and the experience she has over him in such techniques gives her the upper hand. She doesn't have just brute strength she has actual foundation and technique, her strength is a well added bonus. Tsunade isn't activating her seal on the first try, that shortens her life, it's only on a need to basis to use. Yes she'll probably use it but not from the get go. No way is Kakashi going to conserve chakra with Tsunade (you saw how long it took before he stated he was starting feel depleated when fighting pain? not very long. I'm not putting Tsunade on the plain with Pain [ha I made a rhyme

] but I'm saying he's not going to conserve chakra fighting her, he can't afford it the sharingan standard takes a lot out of him). Now beating Tsunade is possible for Kakashi, I'm just saying it's more possible for Tsunade to beat Kakashi. Tsunade was pick number two for Hokage, meaning her prowess is much more then what we've seen (assumed). Because we've seen Kakashi more in battle and Tsunade more at the desk then out in the feild people tend to underestimate her. We have limited knowledge on her yes, but we know her abilities are up to snuff to deal with Kakashi and I see it as a heavier possiblity for her to defeat Kakashi then it is for Kakashi to defeat her (Kakashi knows 1000 jutsu but no way does he have the chakra to use all of them) That's just my opinion.