So, Emily
posted that the assumption is the Grinch banner is the full roster. Who thinks it's real that assumes that, and why could they possibly have any reason to assume that? The only reasonable assumption, to me, is that's the characters that will be released prior to that particular event the hanger is being used at. It's not the banner that will be released on the website prior to launch or in the final Direct (could be, but no reason to assume it has to be the case). It does not directly contradict missing characters--the only real roadblock is adding the missing characters to the banner, that's overboard in terms of how many characters could likely be announced in the final month. The one direct contradiction to the banner would be a character on the banner who's not playable (which is Mystic's reasons for doubting it, and is a much better case against the banner)
If this is the assumption insiders have against the banner--that's exactly the flawed assumption that make me doubt their conclusion in the first place. Having been said, we'll know soon enough anyways, as it only takes one character art reveal to make or break the banner.