The option of puberty (assuming it can be exercised even if the contract was completed by the father) can only apply when the girl has reached puberty. This means that if the parents were to send her to the husband, he'd be able to have intercourse with her because she's "able to endure it" although the actual process of physical maturation hasn't started yet, neither does she have any sexual desire for intercourse, nor does she understand what intercourse means. All that's required from her is to be plump and fleshy. What does the girl gain in this situation? This is the only time in my life where I feel like I almost completely disagree with a Fiqh ruling. This is way too convenient for the male, and in case she were to exercise her khyar-ul-bulugh at the onset of puberty, she'd have already lost her virginity against her own will. What is the reasoning behind this ruling supported by the most wise of the imams and sheykhs whom I greatly respect? JazakAllah in advance
You are asking the wrong question.
Sexual activity during marriage is normal and expected, and what you're expecting is a ruling limiting that. The default state in Islamic jurisprudence is that everything is allowed, and the onus is not on the scholars to justify the status quo here, but on those who are seeking to forbid a permitted action to prove that such a ruling would still be in accordance with Islamic law.
When a child is given away in marriage, this like most decisions made in a child's life is done at the discretion of her parent or guardian, who is already responsible for ensuring that decisions made on a child's behalf are done in her best interests. It is their responsibility to weigh the potential risks and benefits while the child is too young to judge such herself.
You argue that a child has no desire for or understanding of sexual activity, which may be true, but nobody would know better if this is the case than the child's guardians. Forcing a child into a harmful marriage that she is neither ready nor willing to engage in is already a breach of the guardian's responsibility.
However, making a ruling against sexual activity (up to and including intercourse) or enforcing a mandatory age limit on marriage would exclude those young women who do have a desire and understanding of sexual activity from exploring that in a legal and safe manner.
So instead of allowing the husband and wife to explore their own sexuality in whatever manner is most comfortable to them, in their own legally sanctioned marriage and the privacy of their own bed, you are suggesting that this should be forbidden not because of any actual harm that will come of it, but because maybe the child isn't ready, or that maybe her parents married her off in bad faith, despite there already being different Islamic responsibilities protecting against those cases.
Where, I ask, is the wisdom in that?