Minato's performance against Obito and Kurama although an impressive feat still exists within the context of Minato being extremely nerfed due to being drained of chakra and mental anguish even before he begins any combat.


Minato had to monitor and maintain the integrity of Kushina's Kyuubi seal due to the seal weakening during birth. Biwako's statements of Kurama almost escaping during Mito's birth giving process further implies that even Uzumakis with their peak sealing prowess and chains alone aren't enough to effectively maintain the seal during child birth.


Labour ranges between women due to a variety of factors but for first mothers it can literally range from 6 to 18 hours on average sometimes even more. 

That suggests that Minato had to maintain the Kyuubi seal for multiple hours at bare minimum all in addition with the stress of his wife giving birth. We also see on panel sweat on Minato which further conveys exhaustion. 



Additionally, Minato potentially experiences another nerf due to the mental stress of being awake for around 6 to 18 hours, applying chakra to the seal, stressing over his wife, his baby, and the village. Then his newborn baby and wife are put in grave danger by Obito with Kushina essentially being sentenced to death as far as they knew with the extraction of Kurama. Chakra requires the merging of physical and mental energies and Minato's mental state during this interaction were as low as they could ever be.



TLDR:

Hokage Minato during the Kyuubi attack had depleted his chakra reserves due to having to monitor the Kyuubi seal for around 6 to 18 hours during Kushina's labour. He also was probably in the worst mental state possible with everything in his life in grave danger. Thus I suggest that the Hokage Minato we see is him in a massively nerfed state and nowhere close to his full power from the moment he fights Obito or deals with Kurama.





Do yall think Hokage Minato was Massively nerfed during the Kyuubi attack or do you have another intrepetation.

Kyuubi Attack Minato was Massively and Drastically Nerfed.