@nex Not sure if you mean T2 fixed arti, or T1/T3 mobile arti. The lack of a T2 arti equivalent on naval is even more reason for T2 torps to get a boost since it removes an option for counterplay by the defender if the attacker gets a unit that outranges the T2 torp launcher. Battleships perform a better 'firebase breaking' role than T3 mobile arti (as if the enemy gets enough T2 arti then even with mobile shields and larger numbers the T3 mobile arti will generally die before they can crack the firebase) so again even more of a reason for a T2 torp boost. The only thing against is that the attacking naval player doesnt have is a T1 arti equivalent, but then we're talking about not being able to easily beat a fixed in place T2 unit with mobile T1 units so it's less of a consideration.
Currently on land you have far more strategic options, variety and interesting gameplay with defences. See an area you want to fortify? You could build T1 PD but enemy can counter with T1 arti. Then you could get T2 PD to outrange the arti and t2 main tanks, but they could get MMLs. Then you could get TMD to defend against the MMLs (or even T2 arti although it's not a cost efficient counter). If the enemy switches to T3 mobile arti or sniper bots then you could get T2 arti.
Meanwhile your opponent in addition to those options for outranging the T2 PD could just ignore/go around the firebase.
On navy, the T2 torps are even easier to go around on a typical pond because terrain obstructions are rarer. On narrower 'streams' then a naval torpedo launcher firebase is potentially vulnerable to land attack (given torp launchers can't attack land). The value of holding a specific naval area is also (outside of chokepoints) less due with underwater mexes being rarer than on land.
Meanwhile from a very basic balance/strategy game perspective, you're sacrificing the ability to move a unit at all, so there should be sufficient compensation. Even with a small range boost every faction has an answer to T2 torp launchers at the tech2 level that is either similar to MML's answer to T2 PD on land, or even better, and unlike land the naval player doesnt have a T2 arti option (the best it could hope for is T2 arti on the land near to the torpedo launcher but the range of it will be so reduced and is crushed by battleships anyway). As such even if you want to fortify a naval area, you're better to focus on mobile naval units to do it giving less variety in games and in tactical challenges.