What is the response to the claim that it is obligatory to return to the fundamentals of religion and abandon the ijtihad (independent reasoning) of jurists and scholars throughout Islamic history?

The highest authority in Islam is the Holy Quran and the authentic Sunnah of the Prophet. Referring to them does not mean abandoning the ijtihad (independent reasoning) of scholars and the great Islamic Fiqh (jurisprudence). Otherwise, to what understanding would Muslims resort in their affairs? Moreover, demanding that every Muslim engage in direct ijtihad from the Quran and Sunnah leads to great corruption and division within the religion.