Interesting thread, I gotta agree that the Vigilance feels pretty disappointing. If you want support missiles in the later game, the Gryphon is an amazing option. Early game, the Vigilance is just too slow and vulnerable.
Some thoughts from me:
Vigilance can't be too fast, or else it becomes a kite machine. Long range graviton or ion beam in combination with high speed is a potentially nasty (and safe/boring) combination.
If the Vigilance is a fleet support ship then running out of missiles early in the battle is a major downside, so infinite ammo missiles are preferred.
On the same note, unguided missiles are generally not great since the Vigilance is not much of a frontline ship.
The above two points means that the Vigilance will favour low-impact support missiles, like the Pilum or Salamander, maybe someone can make the Breach missiles work with the Vigilance.
The Vigilance should be weak to fighters, this seems like a core part of its identity to me. Giving it ship systems that counter fighters would shore up one of its weak points, yes, but also take away something that makes the Vigilance into the Vigilance.
The way I see it, there are three viable changes:
Increase the speed back to 130, this will increase the ship's survivability at the risk of making it too good at kiting.
Add expanded missile racks built-in, this encourages using ammo-dependent missiles but doesn't actually improve the Pilum/Salamander Vigilance. Maybe it opens up some room for a Harpoon/Sabot Vigilance though.
Reduce DP to 4. If a ship isn't very good, then maybe the solution is just to make it cheaper to field it.
I thought a little bit about turning the hybrid turret into a ballistic turret and sidestepping the Graviton/Ion beam shenanigans that way, then you could safely increase the speed of the Vigilance to something respectable. Maybe that's more of a Vigilance (P) idea though.