Indeed. And yet when we went to Thessia - and spent more time there than on Earth - we didn't see a single non-asari except the Reaper and Cerberus attackers. But I don't see anybody calling Thessia an "asari-only" planet.
The Asari also have Illium, a world recognized as an Asari world that features a boat load of other species who are shown to be alongside their Asari family. Not much on the human side since the only alien we ever see on a human colony is Veetor who was only there to help.
And hey, it could even be Hackett playing it safe and explicitly not wanting Shepard at Arcturus Station in case of the decapitation strike we saw from the Reapers - not putting all the eggs in one basket, as it were.
...You're giving ME3 way too much credit. Admiral Hackett, while voiced by the awesome Lance Henrickson, doesn't know his a%# from a dry ice mine. He says he stakes his life on Shepard's warnings that the Reapers are coming and his idea of getting ready for it.... is to leave a sizable fleet, Anderson and Shepard at Earth and hope for the best. And when the Crucible comes into play, he continually states that he doesn't know what it does or what the catalyst is, yet he also openly states the Crucible is the only means of defeating the Reapers and somehow knows when it's "ready". His reasoning for using a weapon which he has no idea what it will do?
Two centuries ago, scientists faced the same problem in the Second World War. They weren't sure what the atomic bomb might do. Some thought it could even ignite Earth's atmosphere, but they did it anyway.
That is wrong. The scientists did know that the Atomic Bomb would not ignite the atmosphere because they found a glaring error when it came to the actual research. The man who came up with the atmosphere stuff, Edward Teller, forgot to factor in HEAT LOSS in his original report. If you were to not factor in heat loss when researching a simple match, you would conclude that the match would never lose it's flame. So once they factored in heat loss, they concluded that there was in fact no danger to the planet's atmosphere and even went on saying that they would rather allow the Nazis to conquer the world even if there was a low chance of the Earth being destroyed when using an atomic bomb. Well, there wasn't a chance at all of that happening which is why it went ahead.
Yeah, Admiral Hackett is a real thinker.