All of Chassidus is based on kaballah. It is applied Kaballah. It is OK to learn nistar nowadays; in fact, it’s a chiyuv on everyone to learn all parts of the Torah that he is able to. There are many mekubalim, including non-chassidim, who have written this.
Without chassidus/kaballah, it is virtually impossible in today’s generation to maintain a true connection with Hashem.
Don’t pin kaballah on Chabad, although their chassidus is much closer to open kaballah than others’. It’s a chassidh/misnagdish thing, and the misnagdim will not come out on top of this.