Sry to be pedantic, and I do agree with your insight on travelling on Holidays. But I just want to say India is a pretty diverse country, so Holi/Diwali aren't necessarily the major holidays in many parts/sections of the country/population.
That is true. And I am in no way generalizing my experience with whole of India. But, in my experience, I have seen less crowds on Holi and Diwali. And taking flight has not failed me till now.
Cue and Behold. An empty airplane, with a total of 30-40 people in an Airbus 320. I got upgraded to business class for free. There were no lines for boarding. The plane took off on time, landed on time, and all of us could sleep in peace (or do whatever it is people do on planes).
From that time, if I am going home for a festival, it will be the day of the festival.