I don't particularly agree with this. Chalice at 0 stops the pacts that Flash plays, so a first turn Duress to clear FoW and a chalice at 0 and you potentially just screwed the Flash player looking to Summoner's Pact.
Against GAT, I would not hesitate for a second to Chalice at 1. Duress, B-storm, Opt, Ancetral, Disrupt, Vamp or Chalice at 2 to stop Merchant Scroll, Demonic, Dryads, Fire/Ice if they play it, Mana Drain.
I still contest that Extirpate is better against both of these decks, including better in the situations you've outlined. In your Flash example, chalice at zero is only good if A) they have pact and no hulk, and B) you have countermagic that needs protection from PoN. (and C if they have a mox heavy, or lotus hand). In your example you have duress + chalice. So you duress away thier FoW or presumably thier flash (if they can win w/o fow. And you then cast chalice @ 0, shutting off thier pact(s). Now consider you have duress and extirpate. On turn 1 you extirpate thier flash, which dramatically reduces the chance they will win on thier first turn (they would likely need lotus + merchant scroll, or to have two pacts ... in which case you'd be forced to take something else with duress but lets stick to more average hands). Now lets say they use thier first turn merchant scrolling for a 2nd flash, but don't have the mana to win right now - a very typical scenario. Now you go to your turn, and you extirpate thier flash .... how screwed are they? Even if they have a hand full of countermagic, they can't do anything but try and win with sliver beats against an aggro deck.
In your GAT example with chalice at one, you really stop 6 cards that matter in thier deck: 4 brainstorms, 1 fastbond, and 1 chain of vapor. Please note that casting a spell triggers dryad ... not resolving a spell. So through opts into a chalice at 1 is really no sweat for the GAT player. Chalice at 2 is good. But again, this deck doesn't run shops, full moxen, or any sort of rituals ... so to get to 4 mana your looking at around turn 3 to 5. Also your limiting access to Confidant, Grunt, and H/S - all of which are important to winning this matchup.
Now again, consider Extirpate. Extirpate is good (esp along side Seek) because it attacks a decks engine. Against GAT, heres a hint. The first seek you draw, cast it immediatly and seek Fastbond. I know its not as cool as gaing 5 life of a gush, but Fastbond is GATs real "win" card. But I digress - There are at least 5 good cards to hit with extirpate: Gush, Merchant Scroll, Dryad, Brainstorm, Force of Will. The value of Hitting each of these cards changes depending on what is going on. If you've sucessfully Seeked Fastbond, then go for Merchant Scroll. Gush is almost always good, reguardless of if Fastbond is still a threat if you hit Dryad early (who is not that hard to get in the yard with all your dirrect damage), the next target should be Gush. Once you have Dryad out, its hard to build a lethal tog without Gush - and esp hard if you have a Grunt out.
Your probably right about Null Rod through. However, I think Null Rod is still a useful tool. Not so much against Flash or Gat, but against Bomberman. Maybe its worth putting in the board.... and maindecking Jitte's in its place. Jitte is really not that bad right now either.
