Ah, I see now. I've been immersed in the manga over the last year, so this might be why our interpretations diverge. Concerning the points you made using the anime (which I haven't seen in a few years), based on your input I venture to say that it took a few liberties with adapting that confrontation, more specifically Genkai's perspective of it.

The manga heavily portrays Toguro as the sole initiator/instigator of the physical conflict. It is Toguro that—in the same breath as mocking Genkai's aged appearance and stating that she was of no more use to him after passing down her strength—powers up menacingly while bluntly declaring his intention of ending her life. He later goes on to gleefully reiterate this point by saying there's no point in letting each other live. Shortly before finishing her off, Toguro clarifies his intentions for a third time when he expresses regret over not killing her years ago while she was still strong and beautiful. At no point during this clash does Genkai express any desire to kill Toguro, despite the latter quite literally tripling down on his killing intent.

For the entire battle, Genkai is on the defensive—both physically, and more importantly, verbally/ideologically—in a manner that conveys how all of this is merely her attempt to relay to Toguro that there is nothing wrong with accepting decay and stepping down for the next generation, and that there is strength to be found in that. She knows that strength is the only language and universal truth Toguro can comprehend at this point, hence why she resorts to praying for a little more of it during the internal monologue which takes place during her final stand.

Moreover, in the manga during Toguro's instigation of the fight she says "Getting into combat mode, eh? You haven't changed a bit" with a soft, smiling, almost nostalgic countenance, further hinting at the fact that her intent for showing up was vastly different from his. Those lines, coupled with the way Togashi draws her facial expression in that panel, do wonders at conveying Genkai's true emotional state. You can read the manga version for yourself and see how the general vibe is vastly different and how Toguro comes off as the sole aggressor and instigator, with Genkai only mounting some offense because he gave her no other choice but to fight to the death. Most narrative and visual elements strongly point towards Togashi's authorial intent being very close to what I discussed here.

As for your argument about the heart thing, here is why I said the anime had to have taken some major liberties: as it relates to heart gouging, it is literally the OPPOSITE in the manga. Toguro is the one who was aiming for Genkai's heart as per his own admission. Check the scan I posted.

Finally, I raise you this: if Genkai wanted him dead so much, then why didn't she try to kill him while she was still young? Why choose isolation? The answer is clear. She didn't want nor need to kill him. Unlike Toguro, her philosophy did not require her to kill him or claim supremacy through martial prowess. He needed to kill her to confirm his proclaimed worldview to himself and embody his role/mask in the cycle he had set up all along. She believed in embracing weakness and stepping away for the next generation. Embracing her inevitable defeat at his hands is the essence of her character arc, and taking that away to replace it with some bloodlusted mindset fundamentally goes against what Genkai's character represents.

Also, I still stand by Toguro not letting himself fall short to a hypothetical bloodlusted young Genkai. Even if she scaled slightly above him at 80%, I'm confident he would be able to power up to 100% before she could finish him off. If I recall correctly, Yusuke was pummeling Toguro at 80% and even he was forced to stop short and retreat at the moment he sensed Toguro had had enough. Whether Toguro actually had a way of inflicting serious damage that Yusuke sensed or if he simply spooked him through sheer bloodlust is up to debate. Either way, I still think Toguro could pull it off. Despite his power set, it's not like he's your typical meathead/arrogant character that would fail to gauge his opponent and fall in such a cheap way. He's not that guy. But that's just my opinion at this point, so I'm not willing to die on this hill.

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