Introduced “late in the game,” with actual motives and alignment shrouded in mystery, and serves a major role as a foil/object of interest for another character…

Maybe you already see what I’m getting at here.

I don’t really understand the disregard for Mari from the perspective you just outlined, because it also describes Kaworu. Why isn’t he similarly written off by the fanbase?

Mari may be new, and we may not understand that much about her, but that doesn’t mean she isn’t a valuable and thought-out addition to the series. We have very little idea what she’s up to, but I wouldn’t confuse that with poor development; I’d argue that she has a very distinct personality and one that suggests real depth, the same way Kaworu’s speech and behavior — though we get comparatively little of it — implies as much complexity. Hideaki Anno may be wacky, and he is definitely reticent, but rushed he is not. Quite the opposite. I think he enjoys taking his sweet ass time.

I am a fan of Mari because she is passionate, funny, irreverent, and quirky. She’s possibly the only character that can go toe-to-toe with Asuka in a way that she actually respects. In fact, I see her relationship with Asuka as comparable to Shinji’s relationship with Kaworu. I’m biased as a hardcore Asuka/Mari shipper, but I’m very happy about their dynamic thus far, and excited to see where it goes.

I honestly think some Eva fans are disappointed by Rebuild’s direction come the end of 2.0/3.0 and are simply misdirecting those feelings at the glaring bit of novelty, which is Mari Makinami. I urge you to give her a chance. At least until 3.0+1.0.