[Alneyan]

The situation you are facing was working so well it was taken down with the 1.76 patch (or was it the one before?) for SE4 Gold. Since this patch, the Allegiance Subverters do nothing against Master Computers, even when the computer has been destroyed. And you are quite correct in saying there is no defence against this kind of designs (under 1.49), except destroy all Psychic races on sight.

Now we have quite the opposite situation: it is very easy to counter Psychic races since their Allegiance Subverters no longer work on destroyed Master Computers, and they do not seem to have much else going for them (well, they have improved ship training, and decent regular weapons, but that seems to be mostly all).