In the end I actually sort of got Zeheart, though it's not the most likely path for a character to take it at least does make some sense to me now. Zeheart has always been all about the Eden plan even back during Asemu's arc, but never had the means to carry it out and score a decisive victory over the Asuno family, much like his brother. Over time he become more and more obsessive about it, but always retained at least some of his humanity yet again this never allowed him to win. By the time we get to the final all-in battle the chance that it might just slip away ultimately became unbearable to him and he finally snapped, made the decision to take the easiest route to ending the battle, sacrificed his most trusted subordinate and still failed to achieve a decisive victory and that was just the end for him.
Does it make him an especially compelling character to me at the 11th hour? Well yes and no..it definitely makes him feel a little more consistent and tragically flawed since I can now look back to the scene where he had that talk with Ezelcant and say, well Ezelcant just offered him the chance to do the one thing he's been obsessed with more than anything in his life, more than his subordinates, more than Romary or Asemu or anyone that he ever cared about, of course he's going to take it. That though makes him kind of a simplistic and highly morally ambiguous character and brings me to my main problem with this episode which was Fram's part in it. Zeheart clearly became the type of commander that she hated and who valued personal ambition over the wellbeing of his subordinates and while I guess an argument can be made that Fram felt his putting Vagan first still made him a noble commander I'm really surprised she threw her life away that easily without at least giving him a workover of some sort or try to take matters more into her own hands. Maybe you know talk to him and try to get him to see reason at the very least since he seems to value her opinion at least somewhat.
I guess it does lend credence to the idea that Akihiro Hino has some issue with the idea of a female character having the greater influence over a male character in the show cause I can't think of any reason she wouldn't stand up more for that belief considering that she's actually been one of the more aggressive and effective female characters in the show. About the only one that's actually directly influenced the battlefield in a way that didn't just involve dying to spurn one of the other characters development. Still despite falling short by quite a bit, simply for her combat record she's probably the closest thing Age has to a female character that stands out after Millais in Gen 2.