Don't think that it's so much that centaurs are so much better than various other sacred troops, so much as it is that Pangaea has a solid sacred troop where everything meshes synergistically with the nation.
Pan goes marvelously with a N9 pretender, and it has seemed to me that N9 is
the most awesome blessing in the game, at least for solid troops. ( It isn't worth very much for, say, flagellants or other sacreds that are easy to kill. ) N4 may actually be the most cost effective blessing - +1 attack, armor, and damage, losing defense, and most experienced players will state that defense is not particularly important for troops. ( For commanders, especially SCs who will be fighting 1 vs 1 battles, things a re very different. )
More importantly, they get berserk, so a single troop can actually win the battle even after all other troops and commanders have routed. And with N9, regeneration both keeps them alive longer, and reduces the number of ailments they receive by 90% - sacred troops with 6 ailments aren't terribly useful.
So : White centaurs, Machakan hunters, Jotunheim's various sacreds, Marignon's paladins, Tien Chi's sacred cavalry, probably also Abysia's Lava Warriors and Atlantis's Mother Guards all become incredibly effective with N9 or even N4, and I may be leaving some out.
Most of the other blessings tend to be useful only on much more flimsy sacreds, ones that tend to die in hordes. (Water is also effective for most sacreds, but either requires vast hordes of cheap sacreds with a secondary blessing like F9, or the incredible sacred troops like Vans or Tuathans.) For instance : F9 - incredible on cheap sacreds, but most die like moths to missile weapons, any AoE spells such as Fireball, Orb Lightning that hit 1 or more squares, etc.
Does
anyone rely on any blessings other than Nature, Fire, or Water to turn the game? I don't think so.... Okay, a high air blessing can minimize losses from missile weapons - but high armor troops don't suffer that much from missiles anyway, and being immune to missile weapons doesn't do anything when the foes barbarians and other hard-hitting melees troops attack - even militia and light infantry can wreak havok.
Death? I've tried a D10 blessing for an area of effect fear. Didn't work very well, even with Vanheim's Valkyries fearing the enemy archers. Maybe for a nation counting on swarms of incredibly cheap, weak sacred troops, effectively doubling the numbers on the field. Almost useless for the nations with sturdy sacred troops and commanders, simply because the reborn unit is 1/5 as good as the original. Astral : Nice for prophets, sacred mages, etc, but extra magic resistance and even avoiding the first attack doesn't help troops all that much. Blood : extra strength and a death curse that takes effect 1 in 100 times? Potentially useful for Mictlan, and for a nation that has a combination of blood magic and low strength/damage sacreds - ie, not often.
So, seems like one other blessing is potentially potent : earth. Even a lesser blessing allows the sacreds to last longer without being fatigued - not necessarily a huge blessing. But at E9, it's 4 fatigue restored a turn,
and 4 armor. Once again - useless for most nations, whose sacred troops still die like flies when they have 4 armor instead of 0, or 7 instead of 3, but potentially valuably for sacred mages such as Pythium, Marignon, and Tien Chi - keeping them awake, and also helping to prevent them from dying to weenie missiles like shortbows and slings.
But Earth 9 seems
especially valuable for a small handful of nations and troops, ones with high armor and preferably some way to heal wounds.
By way of explanations : Nations whose sacreds have low or medium armor protection receive medioce benefits from having the armor increased slightly. Simultaneously those troops with low armor don't tend to have as much of an issue with fatigue, rendering the extra fatigue recovery moot.
But : Nations whose troops already have a high armor rating tend to also quickly lose their fatigue. So Earth 9 both raises the armor to a point where most weapons bounce off,
and delays the time when the troops are tired enough for all attacks to become armor piercing.
Still, a handful of nations and themes have sacred troops with 15 or higher starting armor protection, and correspondingly high encumbrances. With these, it becomes a question of which is more efffective : high berserking + regeneration, or additional armor + fatigue recovery.
Generally, the answer is : berserk plus regeneration. N9's berserking
almost raises protection as much as E9, and gives added attack and damage to boot, not to mention never routing, regenerating from wounds, and receiving 1/10 as many afflications.
But there are exceptions : Machaka's Black Hunters start with 22 armor; at 26 armor they can be the equivalent of the Monitor and the Merrimack in the US's civil war, especially as they effectively stay at 0 fatigue (4 expended, 4 recovered from the bless).
Tien Chi'i's Red Guard only have 15 protection, becoming 19 - not nearly as invulnerable, but TC can hope for a hero who can heal wounds.
Add in N4 to the E9 blessing, and the troops stay alive a lot longer - and they go berserk and don't rout, as soon as they take damage.
But the real epitome of this blessing is probably Arcoscephale : Heart Guards start with 19 protection, damn near invulnerable once it becomes 23 from an Earth 9 blessing. N4 doesn't help the armor (not sure if N6 or higher's berserk would) but most importantly, it keeps them from routing. True, they can't take as much damage as Abysia's Lava Warriors, or Machaka's Hunters. But : Arco's priestesses can heal their wounds, making Arco one of the few nations that can keep troops around long enough to gain 3 or 4 experience stars before the troops are permanently crippled and useless.
It's the easy healing that makes it easy for Arco to go with a minor nature blessing (as can Pangaea, whose troops heal all by themselves), but even a minor nature blessing is potent, and a full (N9) blessing is often incredible. To compare the minor blessings : F4 is +2 offense. N4, if a troop survives first damage, is +1 offense, +1 protection, and +1 damage, plus never retreating. Only serious drawback is sacred mages going into melee combat.