Why did devotion decks dominate PT Theros?

Question

Pro Tour Theros was full of successful devotion decks, with mono-black, mono-red, Gruul, and mono-blue all represented in the top 8, and the finals being decided by a blue mirror.

Conventional wisdom is that multicolor decks are optimal in competitive Magic due to their broader access to powerful cards, with the occasional exception of an ultra-fast consistent mono-color aggro or combo deck (like RDW or High Tide). And Theros Standard is a format mainly consisting of a multi-color block full of powerful gold cards like Loxodon Smiter and Sphinx's Revelation, and decent multi-color manabases based on shocklands, scrylands, and guildgates.

But the dominant decks at PT Theros all seem to be rather midrange-y de-facto-mono-color lists. Why did that happen?

What aspects of the Standard card pool and metagame made Pro Tour Theros an ideal environment for devotion-powered decks?

Answer 1

Conventional wisdom is that multicolor decks are optimal in competitive Magic due to their broader access to powerful cards

Part of it is that devotion breaks that conventional wisdom, because it actively rewards you for playing lots of cards with identically colored mana symbols. The power level of the main devotion engines — Master of Waves, Gray Merchant of Asphodel, and Fanatic of Mogis — is high enough (when you have significant devotion) that it overwhelms the benefit of running multiple colors. For example, if you already have 5 devotion to blue, then Master of Waves gives you 6 2/1 creatures for four mana. Nothing in RTR block is nearly that good, even when you can put multiple colors together.

Of course, the high potential power level of e.g. Master of Waves wouldn't matter if you had to run otherwise terrible cards to enable it. But the cards that have lots of colored mana in their mana costs, like Nightveil Specter and Boros Reckoner, tend to be reasonably powerful anyway, which is related to the fact that they're normally so hard to cast. Devotion was just the extra benefit these cards needed to elevate them from fringe playables to core cards of the format.

Answer 2

As you indicated in passing in the question itself, the key to the matter lies in the phrase 'access to powerful cards'. Often (though keep in mind that standard environments with very few multicolor cards aren't that uncommon; think of the pre-RTR environment!), the powerful cards are multicolor cards like Sphinx's Revelation; but their being multicolor isn't specifically correlated with their being powerful. There are other 'paths to power' for a card, and one that Wizards dips to occasionally is the extra colored mana cost; consider a card like Genesis Wave (or even more prosaically, Leatherback Baloth where the card is 'allowed' to be more powerful in exchange for stronger restrictions on the decks that can cast them. This is essentially the same tradeoff that's made for multicolor cards, an increase in power in exchange for a decrease in availability; the difference is just in how the decrease in availability is handled. Seen from this axis, devotion just serves as another means of enforcing the same restriction, only requiring the strong committment in terms of permanents/mana symbols in play rather than in the individual spells' casting costs.

There are also some localized metagame factors that particularly contributed. First, mono-red aggro decks were a major part of the pre-Theros metagame, and so cards like Frostburn Weird (as an early blocker that can eat many of the mono-R creatures) and Master of Waves (as a protection card that's almost impossible to get through even without the additional bodies that he brings) are solid metagame choices against that deck even without the devotion aspects.

Secondly, and more broadly: in an 'unknown' environment, particularly a post-large-set new environment, new decks are generally likely to do better than established decks, because it's much easier for the new decks to prepare for an established metagame than for the established decks to figure out which of the new decks are most critical to adapt to. This state of affairs often doesn't last long, though, and once the new decks are better-understood then the existing decks quickly learn which tools are most important for combatting them. This can be seen in the post-PT-Theros metagame, where Esper has taken over as the control deck of choice and WUR has completely evaporated; black removal like Hero's Downfall has proven to be a better option than red burn since it can successfully hit cards like Master of Waves and also conveniently hit a Domri Rade that's already added loyalty. Even the new wave of Mono-Black decks are essentially a reaction to the 'first wave' of devotion decks.