So what you're saying is you form un-validated preconceptions and biases, then judge a work while under the influence of those?
I'm not saying one should be so uptight as to scrutinize a work the moment you pick it up, but what you describe sounds a heck of a lot like lazy and bias-ridden thinking and would explain a lot of false and broken expectations I see on the more exotic manga on the site.
Looking at other comments, both for this manga and many others, you would think that half of all mangaka are purposefully making "funny" unfunny troll stories or are people with mediocre imagination. I think there's some irony in that latter view when it comes from a community of leechers consuming manga like popcorn.
Which is why when someone argues majority within this community, I'm really skeptical at best, like this. Ten's of people sampled from this lot...
If you lot want to bother thinking at all, just remember that these new humans still aren't humans even if they have adopted some parts of that culture. This guy isn't shown to be like class rep in that he's a morally bankrupt person who helps others to please himself, neither is that girl about to reveal she's another alien. Even the final scene tells us something, with architecture that old humans never made.
I'm not going to bother giving more answers than that. It's clear the majority of manga readers want to be spoonfed certain types of stereotypical plot development. Some parts of the final scenes call back to the beginning of this manga, especially the memories, but it's not a cycle, so why show it that way? Ask yourselves that. Or move on to the next manga you find so 'bad' it's 'funny'.