Fair enough, but I don't know that I would say naval UPs would be useless. Sabotaging trade routes is a strategy I employ in every game as a colonial power (which Venice can be considered by virtue of its UHV goal). Blockading large coastal cities can also starve the entire civilization (especially Portugal, England & Norse, who rarely have an inland city, and Genoa & Cordoba/Spain can be severely hurt by such a strategy as well, when Milan/Leon/Toledo/Madrid become their only growing cities).
The human could certainly make large, dangerous fleets, but the AI would never manage to utilise a naval UP. If Genoa gets MR earlier (or starts with MR), what kind of UP could Venice get to still make them distinct to play? Giving them cheaper mercs would essentially make Venice & Genoa the same civ with different UBs.