I like the idea of making the Talisman make ships easier to hit. Or make the thing terribly expensive, as that will inflict cost during construction but also cost during usage.
Hell, you could make the thing make every ship in the fleet easier to hit, every ship in the system if you wanted to. It is possible to penalize the Talisman, but will that ever balance it?
And I don't think
realism is worth much, other than an interesting issue to argue about.