unfortunately, the way VaS is set up, the Navigatoris lose their most powerful advantage over most destroyers in the Med Theatre - their 6 4.7" guns. That gives them the same firepower as any other 4 gun destroyer under the rules, and not quite enough to qualify for the 2 AD of the Tribals.
In effect, that just makes them torpedo boats without enough torpedos!!
how to fix this? take more of them.
As for the Duilios, I like them. what they lose in damage they gain in the number of guns. they're easily a match for the Queen Elizabeths out there. The trento's? no complaints from me. very fast, big guns, long range. With those I'll gladly face down most cruisers in the world. Shame about the Zaras. They come off in VaS as not quite so good as the Trentos. They should have more armour, which was the big distinction. Not much point taking them when you can take Trentos.