The Problem of the Modern Tsundere

I-it figures that you don't understand what the problem is with most modern tsundere characters. I guess it can't be helped, I'll explain it to you. I'm not doing it for YOU or anything, I-I just... It'd be too pathetic if you went your entire life without knowing.

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Right, so the problem, as I see it, with most modern tsunderes is that they are similar to Asuka from Evangelion. The reason this is a problem is that Asuka's dere-dere side is never really displayed in front of the object of her affection, only the viewer. Her character doesn't work in the contexts that one finds most tsunderes.
The MC needs to see and understand that the tsundere is being affectionate in their harshness. Otherwise, they really have no reason to hang out and, in series that force them to anyway, their interactions seem forced and cliched.

This is especially a problem when the MC is dense as fuck. Having a tsundere in the cast means that an MC has to have a decent level of perception to see ANY feelings of affection in most asuka-like tsundere characters. So when they seemingly "get it" it's out of character for them.

Now, it worked in Eva because Shinji and Asuka DON'T really hang out. They spend a lot of time together, but it's not "quality time" they're just in the same places most of the time. The few times when they try to get closer it's awkward (for them as well as the viewer). In a way, Shinji is a tsundere as well, but instead of being prickly (tsun-tsun) in the outspoken way like Asuka, he's prickly because he's hard to approach. In many ways, the Hedgehog's Dilemma is the perfect illustration of tsundere character interaction. There's no way around the spines, so direct attack or complete avoidance are the only routes.

So a combination of shitty MCs and characters who follow the prototype (carbon copy tsunderes) and not the archetype (philosophical tsunderes) are the problem with the modern Tsundere. The archetype isn't outdated.