melee naval units would be the only type of unit that would take damage from attacking embarked melee units. naval ranged, submarines, airplanes, and ranged land units don't face reprisal.
A Tercio has 25

CS and costs

300
A Caravel has 25

CS and costs

350, even though it comes earlier.
So, if melee land units can stand up to melee naval units of their era, they can effectively replace melee naval units of their era entirely. All they have to do is screen for the ranged naval units, who can attack embarked units without reprisal, blockade cities, and they don't have to be able to do much else. If melee land units can defend roughly as well as melee naval units, then they don't really need to attack; you can just ignore the enemy's melee naval units, because they can't effectively hurt your invasion force without hurting themselves, and they are useless once the fighting moves onto land.