Hajime Isayame said in his latest interview that we'll be focusing on the Marleyan arc for a while... So, I guess that we just have to "reread" everything from a different point of view.
Here's the difference b/w Reiner and Eren: While I don't really like either of the particular characters, the reason why I understand Reiner's overly patriotic character better is b/c of his background story. Reiner has been drilled to become a soldier and potential titan shifter since a little kid (before the age of 10). Unlike Eren, Reiner has lived in horrible conditions and been shunned comparable to the Jewish people during the Holocaust (which is what Hajime Isayame trying to imply). Before Wall Maria fell, Eren lived a relatively comfortable life with a doctor as his father. He wasn't discriminated. He didn't live in poverty. And yet somehow, Eren ended up being a child with an incredibly bad temper. I wish, we were at least given a reason as to why he's like this. I mean yeah, once his mother gets eaten, I understand why he's like that, but before that? The argument with "living in the walls" is not convincing enough to me; that alone doesn't causes a child to have such an aggressive character. I'm not saying Eren is inhumane; he's just not a good main character with his main character trait being angry. He seems to have matured though, so yeah.
Oh, and the only reason why I said that Eren will be a terrorist is b/c he's right now spying on the Marleyans. He and Armin have already captured all the other ships the Marleyans have sent to Paradis during the last few years- who knows have many have been killed.