I don't consider them as niche, they are about 1/3 of my navy, because they are great vs other ships, especially when they can hit and run. Also they require different strategic resource. Yeah, building a sub instead of other ship is definitely a choice, but I'm talking specifically about a choice between submarine promotions. If picking the one promotion is the correct choice almost always then it's not really a choice, but a mundane clicking, so what's the point of that? Also AI may make mistakes if it chooses other promotions.
If nerfing Wolfpack would make subs useless, then it shouldn't be nerfed, because then the previous choice (which ship to build) would be less meaningful. However, why not buffing other promotions, so they could compete with Wolfpack? Or Nerf Wolfpack, but at the same time make the base sub stronger (not just in terms of CS, but also abilities), so they are not useless?