After reading through a number of tournament reports, reviewing listed decks, reading through the various discussions here, and testing my own decks while doing some face-to-face play, something is becoming very clear to me: support removal is currently a key component of the metagame.
The reasons for that are fairly complex, and I'm not sure I understand all of them. But one important reason could be the addition of some support cards in recent cycles that are extraordinarily powerful, and that have effects that dramatically influence play for both players. For reasons of their own, the developers' efforts to shape the metagame have often come down to introducing powerful support cards to shape the direction of play. Examples: Khopesh of the Abyss to deal with flooding; Flux Stabilizer to deal with bouncing and resurrections; Snow Graves to deal with discard pile fishing; etc.
Why is that a problem? Quite simply, because certain factions are able to remove support cards, and others aren't. Factions that can remove support cards are therefore able to retain control of the game, while factions that lack support removal are not. What is more, many of the support card effects are triggered effects, so having "slow" support removal - e.g., available only during your turn - is not good enough. It has to be ready, on-demand support removal, or very bad things can happen. Ideally, support removal would be able to target both attachments and locations - splitting removal between attachments and locations is card-inefficient and very often less reliable (removing problematic attachments by directly targeting characters does not work on Snow Graves, for instance). Bottom line, direct support removal is optimal and virtually indispensable.
Unfortunately, direct support removal is readily available to only two factions: Cthulhu and Shub-Niggurath. Virtually every tournament-competitive deck I have seen listed includes either one or the other, and with their ubiquitous support removal cards: Deep One Assault (arguably the best card in the game) and Burrowing Beneath (Thunder in the East is also good, but not as reliable as it is Operations phase only, ditto for Grasping Chthonian). Other factions have support removal that is either unreliable, inadequate (e.g., Silver Twilight's Lodge Housekeeper - congratulations, you have removed a support card for exactly one-half of a turn), or almost entirely missing - good luck removing support with that Miskatonic deck, you're going to need it.
Case Study: The Temple of Mutual Sacrifice
Consider, as a case study, how one would deal with a simple but brutally effective deck - a Cthulhu deck stacked full of Serpents, with Temple of R'lyeh and Sibilant Cry. (Yes, I know; "There he goes complaining about the Serpents again" . . . but seriously, this deck is going to rampage over some unprepared players.) Serpents are flooded out as fast as possible until the Temple of R'lyeh can be put into play, then everything is sacrificed clearing both players' boards (which can be done in one fell swoop in any given action window once the Temple is up), then all the Serpents are popped out of the discard pile with Sibilant Cry and walk to an easy win.
What do? "Snow Graves" is the obvious answer. Except that any half-competent Cthulhu player is going to stack the deck with Deep One Assault and Get It Off, which means he can easily pop off the Snow Graves as soon as he's ready to clear the board before bringing the snakes back from the dead. Likewise for Flux Stabilizer, etc.
That means, realistically, that the only way to shut down the combination is to destroy the Temple - but it has to be on-demand (so that the player can respond when the Temple goes up in the Cthulhu player's Operations phase), and would almost certainly have to be an event card, as anything else - say, a Ritual of Inferno or a Crazed Arsonist - is going to get Deep One Assaulted (again: best card in the game) before the combination gets put in place.
Looking at that, it becomes perfectly clear: you need on-demand support destruction, or just this type of a combination will be absolutely ruinous. That means you either play Cthulhu or Shub-Niggurath, or some combination including them, or you get ruined.
*Three Factions, Actually
OK, actually, there is another choice, and that is to play Hastur and have a Power Drain ready (or just have a two-resource domain with Hastur match available, and just get this look on your face as if you have a Power Drain in hand, that works too).
Hastur is a bit of a special case, in that they have a lot of unique effects - especially related to event cards - that give them a lot more control over the game. Hence, even though Hastur doesn't have that powerful on-demand remove-this-support-card-now effect available, they have a lot of other interesting tools in their toolkit that lets the faction deal with nasty strategies. Power Drain is one obvious example, but in this case they could also, for instance, focus on rendering as many of the Serpents insane as possible, which means they can't be removed by the Temple of R'lyeh as they aren't Cthulhu faction matched while insane.
But that's very specific to Hastur. The other factions, generally speaking, do not have the same kinds of unique tools to deal with difficult situations.
The bottom line is, as important as support cards are, removing them as soon as possible is critical to controlling the flow of the game, and only two factions are really able to do that consistently: Cthulhu and Shub-Niggurath (while Hastur is an honorable mention, as they can frequently deal with difficult situations in other ways). That means that any serious competitive deck is going to have to have one or more of those factions. That stinks, as it limits the versatility of the game and limits the options on deck-building.
I realize that the decision was made to have each faction have some flavor, by limiting certain things - support removal, event cancellation, etc. - to certain factions. But you can't do that and then introduce powerful support cards and event cards into the game - particularly support cards, whose effects are persistent. At some point, if the developers want to balance the game out across the factions, they are going to either have to spread the support removal around, which will necessarily reduce the unique flavor of the factions, or they are going to have to bring the hammer down hard on the more powerful of the support cards, and stop using support card effects to try and balance the metagame.