Very intresting question.... ...how do(es) enlightened being(s) relate to the realms of suffering? Let's entertain the idea that they do not relate in a direct way to the relative truth. That means, like your milerepa quote, there is no cognition of differences between people. No aggresive/sexual Sogyam Rinpoche vs realitively peaceful graceful and asexual his holiness the dalai lama, no talkative president donald trump versus kind hearted muni, etc... all the same...
Are there actually realms through enlightened 'seeing'?
Human is tool to be able to see *the basically kindness of others*, because without
how is enlightenment possible? Even beings suffer and harm, like temporary sick confused minds, their-our nature is same as all enlightened nature, impossible to be different.
Now back to the question. If we want to make reality, what shantideva wished to do, help humans end their miseries, is it better to become enlightened or to be reborn?