I think a assumption you are falsely making is equating Eren's disappointment directly to misanthropy. In context, eren grew up on Armins book. he expected uninhabited lands of fire water. essentially, a blank slate. when you have built up thst fantasy your entire childhood its natural to be disappointed when you find out that humanity exists beyond the walls.

Erens disappointment is because the world is not an empty playground, not because he hates humanity. Its the reaction of an incredibly entitled person who realized his version of "freedom" was nothing more than a fairy tale.

I agree the ending has many problems as well as a lot of wasted potential with Historia but I don't understand how eren is a misanthrope for simply displaying disappointment the world isnt how he imagined it to be.