I dunno if they're INTJs. It was just an interesting speculative starting point. To be fair, I should've been clearer about that/clearer that the claims were knowingly dubious.
Though on Letterman - he doesn't seem extroverted to me. He seems fairly wrapped up in his head. Certainly wouldn't rule introversion out - social introversion anyway. Don't know Hoffman well enough - but De Niro's "concrete" vibe could be somewhat related to culture/ethnicity I think.
I did find it interesting, and I think in general Hoffman's a "warmer" actor than De Niro. Nothing wrong with that... but I usually feel like I get more of the actual Hoffman when he plays a movie role even if he's really good at switching up characters, whereas DeNiro? I have no clue who this guy is, even after watching a TON of his movies. He really just drops into his character.
Watching the interview, Hoffman plays the more sociable interface for the two of them (Letterman and Hoffman even play into it), and it only reinforces my idea that DeNiro is actually a pretty private individual. Not someone who hates people, but he really doesn't seem to get as much into revealing much of his private exterior/interior life to the public. And definitely not someone who "wants to be a celebrity." Hoffman seems like he more naturally WANTS to make a connection with the audience, he's more engaging in a warmer way without much effort.
And yeah, I always got a more concrete feel to DeNiro -- kinda gritty, kinda tangible, you can get your hands on it. Not high-brow ethereal-type acting.