2x Shiva plus a Sulis make a fantastic Squadron. That means potentially 18d Fwd Beam at 20", 9-12d Broadsides, and 9d Torps.
Plus you can peek out the Sulis from cover, and fire the Shivas at full power from effective hiding.
But they're also the best helpers for the Oannes, Raising the fore beam to 18, and Torps to 10.
A squad like that would replace the Sulans admirably, but you lose the horror of those Grav weapons. :-)