Indeed we do. A torpedo bomber even was in the game files at one point. Would make for a great specialized T2 unit...
Not really. The difference between a regular bomber and torpedo bomber is kind of semantic. They both drop big payloads to hit things underneath them. Now, a T2 amphibious bot/tank would be pretty useful. There are at least three major variants to work with: The first is a land raider that just happens to also travel underwater. TA attempted this with the Triton, unfortunately the vehicle was too slow and vulnerable to naval interception to be of any real use. The second variant is a type that specifically attacks water units to reclaim the sea. Chances are you won't have naval control and are specifically using this bot to reclaim it. Therefore the role is best accomplished with something slow and heavy (trench walker) with lots of anti-sea firepower. The third variant is some kind of hover vehicle that doesn't distinguish between land and sea. There isn't much difference between this and a walking boat. However, this unit class emphasizes the importance of keeping homogenous balance metrics between the two theaters. Fifty metal worth of power out of a land factory should not be remarkably different from 50 metal out of a sea factory. That's how you break things.
I can imagine a torpedo bomber being quite diverse from a regular one: - Torpedo bombers can drop their payload way before they are above their target, effectively increasing their attack range and making them more safe to AA (the torpedo travels by itself underwater after being dropped) - Torpedo bombers can hit the underwater and seafloor layer (in this case regular bombers shouldn't be able to) - for this to be effective we would have to have submarines and more amphibious units, maybe even underwater structures - Torpedo bombers could deal increased damage, as they are limited in their choice of targets and deal no AoE damage