Yes I prefer a disperse effect here because it is better to play catchup or to protect your key enchantments. And as you said, dispersing an Oath is a cheap way to get more mill in. It's close though.
I play oath over Pore just because its cheaper. The deck has alot of stuff to discard, and planning your turns is often more important than getting value. Izzet can't be a full control deck like Jeskai mill can, you need to be proactive, waiting for t5 draw power is a bit late, even if you get 2 mana back.
Part the Waterveil is often just discarded, but with the card selection this deck has you can afford to run this I think. It is perfectly able to close out a game out of nowhere even without any ramp in the deck if your opponent is playing some control variant and didn't play around it, and at worst you are basically playing explore + mill 2
I'm biased towards Judgment. The deck has the axes, chandra, defiance, oath, reveler, sanitarium, and to hand discard as a way to get it off. it doesn't truly 'shine', but it's hardly ever a truly bad card, I'd say on average I manage to discard it for value and burn for 3; and in my opinion its polyvalency makes up for the mediocre payoff you sometimes get. I can ping small dudes, spread some love if my bombardment or axe can't quite kill a dude, I can chaingun a big board, I can hit walkers whilst getting value back; it's like the other 1 offs. This deck has alot of card selection and the geistblast package makes me want to have access to alot of different effects. Geistblasting Judgment isn't a thing, but the other 1 offs do get forked often, and having access to another unique effect in my wheelhouse is something I enjoy greatly.