By that logic, we should remove /dep/ because people will only cry about not having a succ. In reality, it never happens because there's a rule against it. The same way depression doesn't have to be about not having a gf, self-improvement also doesn't have to be about getting one.
Crabs here are actually some of the most vocal anti-improvers because they get immediately triggered at the sight of another male working on himself. They are incapable of seeing past social/sexual hierarchies and are determined to police this place in order to manage their crippling inferiority complex.
Having said that, an entire board dedicated to /sig/ would be overkill. I think it's enough to have a containment thread on /hob/, provided mods would be willing to keep it on topic and delete crab shitposts. There are already dozens of threads that are implicitly about self-improvement, like the fitness and many hobby threads where people want to improve their skills. However, the /sig/ would be nice for discussing self-improvement in broad terms, various techniques that can be applied cross-domain, as well as the general psychology/philosophy of self-improvement.
Self-improvement can co-exist with the wiz way of life, provided you aren't talking about how to pick up chicks or the best sex positions. It also doesn't have to be normie-oriented, since one could wish to improve at a game or better control his sexual desires or even one's crab mindset.