It is stated that it's on par with anti-matter, if not a little worse. Whilst it may be absurd in your eyes this is still sci-fi and the reason the Solar Empire uses Xalium is because it's more economically possible, the Xa18 anti-matter reactor does however do as you state, however it's created by the greatest mind in the entire solar empire and yet again, there's one of them. If you're going by the logic of current times you should just stop mainly because the Claudian's have excisted for a while and you cannot apply current day logic to a nation that is present in an advanced interstellar technological state.

That is my own opinion, anyway.