“But I’m curious if any of those who believe “Hareidism” is indeed a “modern phenomenon” can name any of the founders of this new movement, and how their beliefs differed from those of their teachers.”
The Brisker Rav, Chazon Ish, Reb Aharon Kotler, and Satmar Rav, were all charismatic and influential people who had some significant chiddushim in their mehalchim.
That’s where a person who believes as above might start pointing. #justsaying