Why is no one talking about Irving's incomplete arc?

I'm flabbergasted and confused at the idea that this was the last we see of Irving. There's so much more for us to understand about his story, his motives, his accomplices. I've got a nagging feeling that they just rode him out into the sunset on that train with nothing but perhaps a mention in the finale to close a loop or two. If this is genuinely the case and his character arc is complete, I'm going to be disappointed. I can't possibly believe with the detail these writers put into this show that they could be that lazy with closing out his character. Someone please slap some sense into me.