What is the main success for an Ethereum project that solves something that can't be solved without crypto or in a hugely more efficient/better way? I'm a crypto skeptic and I've never been introduced where crypto actually solves a problem.

Read the GP comment again. I don't know if Ethereum has, is or will ever get to whatever grandiose goal they have. But the one thing that I love has done is provide intelligent people with funds to research things like ZKSNARKs and similar cryptographic constructs.

It's like war: We don't like war, we don't like people being killed, but man, the amount of technology progress made during war is good.

So, even if you hate crypto; the fact that it is enabling research in cryptographic theory (even if for stupid goals) is good.