That makes zero sense. Byakugo being active and simply having the seal in itself boosts her physical abilities and her chakra levels as seen by Sakura's chakra level and physical abilities increasing after forming the seal WITHOUT her actually releasing it. That is restricted here. So no, she doesn't have the stamina to fight 5 Susanoo clones without her Yin Seal. Only thing that doesn't change is her SKILL in Taijutsu, overall prowess is a combination of skill and physical ability and Tsunade w/ the seal>Tsunade w/o the seal in physical ability and it's not even close.
Given the fact that Sakura's seal formed mid battle that would imply that she was not directing all chakra into attacking and rather was diverting chakra into her seal formation. When the seal filled, it all normal chakra that had been diverted to the creation of the seal was again accessible. The unopened seal has nothing to do with Sakura or Tsunade's ability to attack. Generally why one must open a seal. To access what's inside it... So you're wrong, drarastically. Tsunade not being able to use her seal makes her more powerful as her tremendous base reserves can be used without diverting chakra whatsoever.
This isn't Tsunade without the seal this is Tsunade not using the seal, which is a notable difference. But her strength and overall chakra may increase with the seal. But, as Orochimaru noted in part 1, her base strength is great enough to kill. So that's a moot point. And in part 2 her chakra feats blow Kabuto's out of the water to the extent that talking about the chakra boost she gets from the seal is also unnecessary.
Also you misunderstand stamina in this context. There is chakra stamina to which I wasn't referring to, and there is physical energy. Which would be why I mentioned huffing and puffing... Tsunade has enough Stamina of the second variety to fight at that level. As compared to Part 1.
Further when Hashirama compares Sakura to Tsunade, there is no way in which he can be referencing the Byakugou technique. As Sakura wasn't using it, and he'd have 0 knowledge on it whatsoever.
That's all Tsunade with her seal. So Part 2 Tsunade w/ Yin Seal>>>Part 1 Tsunade w/ Yin Seal in terms of stamina. Doesn't mean that Tsunade without the added benefits of said seal has far more stamina than her Part 1 self w/o the seal. And Tsunade only said that when she had to heal wounds inflicted by Kabuto's chakra scalpel. Only Onoki would have injuries as bad as that due to the meteor. The rest just used up their chakra. The more severe the injury, the more chakra needed to heal.
Tsunade did not use her seal to replenish Oonoki and Gaara's chakra nor did she use her seal to heal Mei. So I'm a bit puzzled. We've seen Tsunade open her seal 4 times to use chakra directly from it. She has never been able to use chakra from her seal without opening it with the exception of Katsuyu, which isn't restricted but she doesn't need it to turn Kabuto into Pâté.
The meteor left such an impact that Madara regenerated from it. And he was further from the meteor than Gaara... just saying. Gaara likely received some injury. Though I don't care to spend time on that point, as she refilled both of their chakras while she was in base. And given the jutsus both Oonoki and Gaara were using that alone is impressive enough to say she won't have to resort to her seal. To outdo Kabuto with chakra. Then add in Mei, I'll let you decide if she was treating wounds or refilling her chakra. It doesn't really matter as it was still her base form.
It boosts physical ability, so using that as a feat for Tsunade w/o the seal makes no sense. That's like me saying "KCM doesn't boost Taijutsu itself, so KCM Naruto and Base Naruto would perform the same or roughly the same in a Taijutsu fight" even though KCM boosts Naruto's speed and strength. Sharingan also doesn't boost Taijutsu by itself, but due to the fact that the opponent's moves can be read Sasuke w/o Sharingan would be stomped by Sasuke w/ it in Taijutsu and they would perform drastically different against the same opponents.
And no, she herself was never shown pushing Madara in close quarters. All you see is her punching Madara's clone.
And finally no. KCM is not analogous to Byakugou. As KCM is another ability not at all in the same vein of enhancements. Neither is sharingan. The byakugou seal itself simply stores chakra and allows Katsuyu a way to telepathically use chakra to heal. Tsunade can use that extra chakra to add more power to her punches, to regenerate, perhaps shunshin, though she's shown no sign of using shunshin. But to say it boost physical ability is a over generalization that becomes your strawman because its easier to attack. So, I'm puzzled when you say you don't know how to interpret Tsunade's taijutsu when the seal was active. Her punches were stronger but that really has little to do with prowess. So again, that's just not valid.