@moorebrother1 because it's not blue and it's way worse in a topdeck war. The CA is the same (Probe +0 for you, Phyrexian Duress -1 for you -1 for opponent = 0). That's basically it. There are other things that make discard not that great, but those are covered above and in Reid's article.
There is a strong assumption with some the replies that the deck would be blue based. What if the deck were only black without any blue cards.
Black is strong enough and broken enough to work without the blue cards. It is missing the counter magic. Looking at all of the removal available to black and the broken draw spells I think there should be more black in the metagame.
I know Dredge is basically a black deck, but what about something else?
I think the issue is that if you have duress and thoughtseize in your deck your probably playing a fair game, possibly without reactive counter magic. You will have a hard time dealing with the really broken fast decks. A good example of a duress deck done right is DPS. You can duress against the slow decks and your deck is fast enough to not worry about other fast decks so you don't care that you don't have FoW ~ect.
If I was building a deck today to primarily use Duress effects I would wan't either a really fast deck, or a deck that could cast 2+ Durres effects from turn one on and had Sensei Tops and cards to keep me out of top deck mode.
I use discard a lot in my decks. I'll have to say, I loathe blue, so my decks tend to be GBW or some variant thereof. In my oath deck, I run 8 duress. In my Depths deck I run 5 or 6 depending on the day (and sadly, 2 missteps as a necessary evil vs swords to plowshares). I think I know why duress effects have fallen out of flavor.
Counterspells obviously are a replacement blue utilizes, but as pointed out, blue decks once used discard. But now decks have become incredibly cantripy and redundant so that if a spell can't resolve, it is no big deal because the next card cast is similar in power, In earlier days, or in certain decks, punching through a key spell required duressing to remove the counterspell or see the coast is clear. I think many decks now are not looking to punch through a key spell, but rather resolve several incremental advantage spells so that by the time they are ready to win, you've been buried in CA. Even non-blue decks like dredge and shops are just a bundle of redundancy that don't care about a particular spell resolving. There are fewer "combo" decks or decks hinging on a single spell breaking the game as there once was. Even PO decks don't need to resolve PO - everything they cast is en route to drawing far more cards than the opponent can handle before winning. Oath is probably the closest thing we have to a key spell...but these decks now run S&T, planeswalkers, and castable creatures to ditch the need to push through the oath.
My decks tend to be more combo-centric and bomb related. I run 4-6 tutors in any deck because I prefer to find THE card I need rather than draw 2-3 random cards off the top. As such, I need 5-8 discard spells in these decks. If decks in the meta ever return to more key-card decks, we might see more discard. However the variety of cantrip/draw spells are so vast now and redundancy so ubiquitous, I doubt we'll ever go back.
@moorebrother1 this would be in the realm of a Dark Depths deck.
Also, I stopped running discard in any deck I played that didn't have a quick combo finish, like AdNauseam tendrils, or heavy disruption like Humans.dec to make up for/maintain tempo.
Take Thought-knot seer as an example. I can turn one TKS and I'm way better off than if I turn one Thoughtseize. Simply because of the threat it provides. Even if the opponent deals with my TKS, the opponent is playing into my game now.
my two cents.
Here's a cute data point, for what it's worth. I spent most of the day today testing some Battlebond tech @Aelien . We weren't explicitly trying to react to this thread, but our results are probably relevant to the discussion
The Mind Twist was very good for me, and the Duress effects were very good for Aelien. At no point were either of us sad to be running those cards. I think these cards are still quite good against Combo, reasonably good against Slow Control, fine against Tempo Control, and bad against Workshops and Dredge. I think what one does with a Duress is so different than what one does with a Mind Twist that you have very different requirements for wanting them, and I think what one does with Hymn to Tourach is just something no Vintage deck wants.
Ultimately I think if you're just looking at playing one of Ravager Shops/Jeskai Mentor/Esper Outcome/Inferno Oath/Dredge, in a field that consists mostly of Ravager Shops/Jeskai Mentor/Esper Outcome/Inferno Oath/Dredge, discard effects just aren't the best option over alternatives (with the exception of Cabal Therapy, possibly Unmask out of Dredge decks). That's going to include most players in most metagames ... but I do think there are reasonable decks outside that list, and reasonable metagames that diverge from that list, in which Duress/Thoughtseize/Mind Twist are good choices. Hymn to Tourach, I think, won't make the cut in anything reasonable, and I can't think of any other discard effects that are particularly notable.