Won't change it. The ship isn't meant to be balanced, that's the whole *** point.
I get the general point of the relic ships, really. You only find a handful of them in the whole campaign, cost an eye and a liver to restore and simply must be delivering something in return.
Their performance is great but it has obvious drawbacks (congratulations on that actually, they do feel very flawed without support) for all but one ship, and that's the Valhalla. That said, I am certainly in no position to tell you what to do with
your mod.
The only productive thing left for me to say is that you should change the way the AI handles the Valhalla's Reality Shell. It currently uses it as if it was a temporal shell or a boost of some sort and spams it as soon as an enemy is spotted, wasting it 90% of the time. All the other relic ships actually handle pretty well in the hands of an AI given it's got proper weapon groups and is decently aggressive.
My suggestion is that the AI could use it just like High Energy Focus or Accelerated Ammo Feeder and only activate it whenever the Valhalla's weapons are in range of the enemy. That way the AI will start shooting, activate the ability, spam all of its weapons on the target and when the ability wears off the ship is again in a position to start firing again with its flux at zero.
The icing on the cake for AI using Reality Shell would be to override the ship's aggressiveness to reckess (if it even can be done) since the ship is going to come back without a iota of damage and the more it chases the enemy to do damage while it's active the better.
Edit: added some more thoughts and corrected the typos I could find.