Is it considered unjust to divorce a wife whom one married despite seeking guidance (Istikhara) and the initial rejection of the family, and then feeling aversion towards her after marriage due to a lack of aesthetic desire, which has led the husband to feel remorse?

If you envision divorcing your wife, then that is your right, and you would not be unjust to her. Divorce is permissible, especially if there is a need for it. However, if she is a righteous and upright woman, and you are able to keep her in your wedlock, thus protecting her chastity and treating her well, then this is good, and perhaps Allah will bless you. You may also marry another woman if you are capable of being just between the two wives, which is a condition for polygyny. The true outcome of Istikhara might be the completion of this marriage. The mere fact that a woman is divorced, elderly, or has children is not a religious impediment to marrying her. Indeed, the Prophet, peace and blessings be upon him, married Khadijah, who was older than him, and Umm Salamah, who had children.