I think you are off on your analysis of the Temple build. My Temple build can and does handle beat down well (whether solo mage or mage plus big creature). Your analysis of the Temple of the Dawnbringer is off because you don't account for it's best feature, the rerolling of Defense dice.
The Temple of the Dawnbringer can be thought of as a fractional Block.
The best case scenario for the Dawnbringer is one of these two:
1) Attacker rolls unusually high (critical 2's). You reroll his dice, and they come up unusually low (all 0's).
2) Attacker declares an attack. You roll a Defense and fail. You re-roll the attack dice. Your Defense succeeds.
Either of these cases are,
at best, equal to one Block. (4 mana value) However, both of these cases are far from guaranteed. In fact, scenario #1 is incredibly unlikely (although I have seen it happen) and it doesn't contribute a large % of Dawnbreaker's effectiveness.
It is easy to calculate the additional Defense chance that a Dawnbringer gives you:
A standard 7+ Defense is exactly
50% chance to Avoid. Therefore, there is a 50% chance you will need the Dawnbringer. If you use the Dawnbringer, there is a 50% chance you will succeed. Therefore, a Dawnbringer has an overall
25% chance per turn of functioning as a Block (4 mana value).
Basically, a Dawnbringer is not mana-efficient until it has successfully turned 2 successful attacks into blocked attacks, which on average will take 8 attacks against a 7+ Defense.
The Dawnbringer is extremely efficient over the course of a game, but it is highly inefficient for the first few rounds it is out. This makes it rather similar to Mana Generators - it's good to have, but you don't want too many against a beatdown deck.
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For a Priestess defending against a rush, it is much stronger to combine Stun/Daze with one or two temples, instead of investing very heavily on temples.
If you commit the mana to a Cobra Reflexes (9 mana) + 2 Dawnbreakers (16 Mana), you've spent 25 mana for a "guaranteed" defense against 1 attack, when a beatdown deck can throw 3 attacks per round at this point. (2 creatures + mage)
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On second thought, I think we are actually agreeing with each other. You're saying that a stun/daze heavy build with 1 dawnbreaker temple is really effective against beatdown. (I agree)
I guess my OP was more of directed toward the common (mis)perception that there is a super overpowered "Temples Build" that stacks something like 3 Bimshallas, a Dawnbreaker, and a Temple of Light.