We know that the Umayyad Khilaafah started from Hazrat Mu'aawiyah radhiyallahu anhu, and it was regarded as a Dynasty rather than an actual Khilaafah

Answer

The meaning of Khilaafah has been misunderstood. If the ruler governs according to the Shariah, he will be a legitimate Khalifah of Allah Ta'ala via Rasulullah (Sallallahu alayhhi wasallam). All the rulers of the Bani Umayyah and of Banu Abbaas and the Uthmaanis (Ottomans) were regarded and accepted as Khulafa.

The method of appointment is not a condition for the validity of Khilaafate. Whether the Khalifah is appointed by the prominent Ulama, or by an existing ruler, or he assumes power by force of arms, or by a military coup, he will be the legitimate Khalifah as long as he governs strictly according to the Shariah even if he is a faasiq/faajir. The Fuqaha of Islam never questioned the validity of the Khilaafate of Bani Umayya and Banu Abbaas despite these being monarchies. Monarchy is not nugatory of Khilaafate. The objection which anyone had with Banu Umayya rulers, for example, was on account of their zulm, fisq and fujoor, not because they were the effects of a dynasty. Hence, there is Ijma' on the validity of the Khilaafate of Hadhrat Umar Bin Abdul Aziz. This is because he had restored the Minhaaj of Khilaafate to that of the Khulafa-e-Raashideen. The Minhaaj is the Shariah, and the special feature which makes the Khilaafate of the Khulafa-e-Raashideen outstanding is the simplicity.

While simplicity is laudable and necessary, it is not a condition for the validity of a Khilaafate. Thus, if today the tyrants of Saudi Arabia, decide to implement Shariah Law 100%, we shall be the first to proclaim the king to be a valid Khalifah regardless of the method of his appointment. The method of appointment is Ijtihaadi and depends on circumstances which are ever changing.

The Khilaafate of Hadhrat Ali (Radhiyallahu anhu) whose son Hadhrat Hasan (Radhiyallahu anhu) succeeded him was the beginning of a dynasty. There is nothing un-Islamic about this. Hadhrat Muaawiyyah (Radhiyallahu anhu) perpetuated the dynasty system, and there is nothing wrong in this, for Allah Ta'ala had created monarchy. The Qur'aan Majeed states clearly that Allah Ta'ala had made Mulook (kings) in Bani Israaeel.

The Maqsad is to govern according to Allah's Law. Thus, the ruler who fulfils this objective is a valid Khalifah.