You forget Sunstrider's Flagship in LTA/LTF, which works as a transport ship and a melee ship at the same time - but I kinda agree, naval diversity is not given. Remember from Azeroth Wars: Cataclysm/WotEW the Doomships, which Horde could train? Basically a Battleship with long artillery range. Would be kinda interesting to see Dark Green and Red being able to produce these at some point, maybe in a nerfed variation (so they can't target buildings or at least not important structures). In general a lot can be done. We know for example that Garrosh's Horde also enslaved Kraken and other monsters for sea battles. Water elementals were in LTA amphibic units - same could be done in KTA as well in terms of defense mechanisms for Theramore without making it too crazy of a fortress. The Horde in Warcraft 2 also utilized sea turtles for naval combat, while the Alliance had submarines. So, I kinda agree - naval warfare potential should be bigger than in LTA/LTF.