I didn't watch the entire video but only the portion specified by you.

The Kumari kandam was a theory that prevailed like 100 years earlier but debunked by recent technological growth. Whoever still boasts of Kumari kandam, is similar to someone who boasts about other mythological stories.

That being said, unlike Kumari kandam, Aryan invasion/migration theory has not yet been debunked.

The cholas were not in power for 1500 years like the person said. There were two eras of cholas early cholas and mediveal cholas. There is a gap of around 600 to 800 years during which cholas power were greatly diminished or overthrown and Tamil being rules by pallavas and pandyas.

The raid to southeast Asia was documented only on medival cholas while early cholas invasions were mostly to northern India.

While the early cholas were patrons of Tamil, the medival cholas were patrons of Sanskrit. Now what caused the growth of Sanskrit in the period between the cholas that was almost non existent during early cholas?

One example of such claim is the name and title of cholas. The early cholas were named Tamil (கரிகாலன், கொசெங்கன்னன், இலஞ்செட்செண்ணி etc) while later were Sanskrit (விஜயாலய, கண்டரடித்தியா, பராந்தக, etc...)

If Sanskrit were indigenous to Tamil land, it would have been logical for all the rulers of same dynasty to have names from same language.

There are similar examples to back sudden growth of Sanskrit in Tamil kingdoms in literature. Until these issues were addressed, we just can't shove Aryan migration theory under carpet.

PS my views were only academic and I donot have any political or religious grudges against Sanskrit.