When the K. Kamaraj faction was kicked out; politics, bureaucracy and whole Indian polity was left open to the scourge of sycophancy and corruption. Indian bureaucrats in Pre-Independence and up unitl Nehru era used to be men of honor with a firm belief in the Indian identity and the need to take all people together for socio-economic reform.
Since you blamed that only the post Nehru era is opportunistic i would like to mention why the split happened between Pakistan and India, Jinnah was a prominent leader during the pre independence era and he was the top leaders in INC and we all know what happened when Jinnah was arrested by the British, there was an entire shift in politics with religious polarization being the topic on who will head the movement forward and those factions led to the split. If not for the opportunistic shift in power in the name of religious polarization there is no way that would happen in my opinion.
PS: I am not into any political affiliation but stated what i read from historical data which is available.