I'm not saying that the decision to kill off Miko per se was going to generate backlash- more that all the necessary steps to make her rapid development look at least superficially plausible, and get her to the point where she could be poetically terminated, did- specifically in the form of numerous, raging and perpetually-recurring moral-justification threads.
I think the early version of the character, while absolutely flawed and deserving of critique and challenge, was reasonably clearly a decent person, though I can't really say if she maintained a particular position on the alignment barometer up to the end. I broadly agree that the 'LG antagonist' bit didn't really work, since Miko became 'villainous' to the precise extent that she started ignoring both L and/or G.
In a certain sense, I can imagine that a version of Miko who started out less clearly nuanced, competent and sympathetic might have been less of a problem, in the sense that you'd have fewer people rooting for her, and the transition to villainy would be smoother. I'd probably prefer a version who's gradually reformed, in the same sense I'd prefer the main protagonists behave less like a pack of squabbling children, but would I prefer Nega-Miko to endless Miko-bashing? ...You know, I might.