No one ever complains about Spock being the only alien in the crew in TOS.
That has to be looked at in the context of when the series was made, when a culturally diverse human crew was of more significance than aliens.
Ent was a prequal to TOS (by 200 years), so it actually may have been more realistic to show no aliens as part of the NX-01 crew. But just because Ent was produced some 50 years after TOS, doesn't mean that the prequal should appear more culturally evolved (with respect to aliens) than it's "sequel" (TOS). Indeed, it should not.
But Dream's point, I believe, was that people who complain that there were not enough aliens in the NX-01 crew usually don't have the same complaint about TOS having only one alien crewmember. It implies a double standard.