HARJOT

Small Confusion. Why does Aizen has to go to Hueco Mundo to open Garganta? Can't he simply open it on the FKT?

Bro, I only stated that Mugetsu state should be considered stronger than TYBW arc Ichigo because of it's untraceable and supreme dimensional power. I didn't actually mean that Mugetsu Ichigo is absolutely stronger than TYBW Ichigo's Final Bankai. Since, in TYBW arc, Ichigo has all his powers: Shinigami, Hollow, Quincy and Fullbringer all combined in one but yet he was easily sensed by other Shinigami's like Ikkaku, Yumichika, Rukia and others in whole Final battle arc. There was not a single moment we know where he was said to achieve a state where his spiritual energy was completely untraceable to others. Despite your statement that Ichigo must have achieved Reiatsu of atleast equal or higher than Soul King merged Yhwach, he still didn't said to achieve the state level of Mugetsu Ichigo, a complete and absolute untraceable state. And last thing, we didn't know what is full potential of Mugetsu state, since its'sthe temporary power which Ichigo achieved after sacrificing his all powers to gain dimensional transcendence. But what could be the potential of Mugetsu state is till unanswered, since Ichigo loss his all powers afterwards, which maybe includes his all four power, let it be Shinigami, Hollow, Quincy and Fullbringer.

Didn't Kyoka Suigetsu activated when Aizen is outside of Seireitei, either in Rukongai or even Hueco Mundo?

You're correct about Aizen of TYBW being stronger than FKT arc Aizen who was just evolving, but don't forget that Ichigo's Final Bankai was repaired in window of time by Orihime and Tsukishima, I don't know, it's still confusing for me if in the end, the final strike Ichigo landed on Yhwach was his Bankai or just Shikai, but it's still stand for the fact that even normal Shinigami were easily able to sensing Ichigo at that time, even in his Horn of Salvation Bankai state or Tensa Zangetsu in TYBW arc all the time. There was not even a single moment where it could be said that Ichigo temporary in a state where he can't be traced during TYBW arc.

Battling? Big words, they're currently only fighting in power “saving mode” till now.

Obviously it should be Mugetsu Ichigo state being more powerful afterall his final Bankai state in TYBW never demonstrated the same overwhelming, or unquantifiable ''dimensional transcendence'' that the Mugetsu form did against Aizen. And not to mention, even other Shinigami's, let alone Yhwach, can sense Ichigo in his Final Bankai state, but Mugetsu Ichigo was untraced, so I will always favoured this state over the one in TYBW.

I momentarily thought that Uchiha Coup is solved what would Danzo think about it now, then I remember that he was dead long in this fic... huu my mind, confused with other fic's stories.

I doubt many of them even know who Ryūken Ishida is...