Nukesub tmls are stronger than you think because of the massive range they have. Its not uncommon to have 5k mass killed just from the tmls (if you havent disabled them to hide your subs) and for a secondary feature thats already quite powerfull.
Also, why are naval nukes more expensive than land nukes if they are weaker? This discourages their use.
Unless FAF changed anything, regular nuke costs 12k/1350k, sub nuke costs 16.8k/1764k: