I think the idea of mixed species living together is fine in theory, and I've seen it work on a small scale, a town here a settlement there. But when the Votans came, Earth was reaching its limit in land and resources just to support the human population. Add the population of the multiple habitable planets of the Votanis System to that, and it was never going to work. Not without an enormous drop in population. Which, in the end, is what we got.