Nice point sjaminei, i forgot about double strike, yeah that one is basically crushing blow without being dazed in the next turn and available to all kind of weapons.
That being said, sjaminei problem is because of they are Tarth, Tarth ranged units are twice more dangerous than other faction (excluding any custom one), not because of you can pick nature cloak or any elemental resist buff, i mean Tarth can fare better against any elemental resist buff than other faction because they do 2x damage of other faction via double strike, hence why i believe sjaminei problem is because of he go against Tarth.
Regarding essence fortress, it's not because it is essence fortress, any town that has high essence and used with battle boosting enchantment (Like heart of fire and its kind) is OP, fortress being better because of it can boost the accuracy of the unit. This case is already exist since vanilla FE v1.00, at that time most people say Pariden being the weakest faction which i totally disagree because Pariden can exploit this essence the best (scrying pool + those 4 tomes), but the vanilla Altar is still the most OP faction.
Regarding crushing blow, it's not a problem if you just use 1, use a couple of it and it's overkill, much more than impale or cleave, this is only in ridiculous or insane (especially in insane) when enemy hp is very high, however in lower difficulty it is a different story. And another advantage of crushing blow is it can go against better teched faction, cleave and impale struggle more against better teched faction (especially lower weapon vs higher armor), but crushing blow will streamroll it, especially using elemental hammer (or using heart of fire). I don't need to play the game to know this, simply by looking at the math that crushing blow is damage x2 first than reduced by def is enough proof, while cleave and impale is directly reduced by def. The solution presented by sjaminei is exactly what i said, crushing blow get def check first then its damage is multiplied.
Another advantage of crushing blow is it has slow initiative, ok this is not the advantage of crushing blow but it's hammer weapon advantage, but because crushing blow is for hammer, i'd also consider this as the advantage of crushing blow. Being the slowest of all melee weapon, those that use crushing blow can take advantage of it by focusing on traits that boost defense (+3 hp and +10 defend when defending is good), why? because each combat units now start in defend mode in LH, being the slowest crushing blow unit will be in defend mode hence allow them to receive fewer damage than other weapon wielder, then when the crushing blow unit strike, other weapon wielder will always be in non defend mode, thus making them receive higher damage, add crushing blow to this and you know the result.
Want to take advantage of it further? make a fast spear or axe wielder (focused on accuracy and initiative), 1 or 2 is enough, the rest is hammer wielder focused in initiative and accuracy and give it traits that give +25% damage against damaged enemy, add them together in a same army, when in combat, make sure all cleaver/impaler act before enemy units act, cleave or impale as many unit as possible, the purpose of this is to damage as many units as possible to make hammer wielder traits always trigger, therefore when the hammer wielder (crushing blow unit) act, it's damage will be boosted by 50% more for a total of 250% (thanks to the traits and crushing blow which multiply the bonus by twice) and this will guarantee them being one shoted (expert difficulty or lower) or one hit dying (higher expert difficulty). 200% to 250% seems not much, just 50%, but please remember that this 50% is calculated before applying enemy defend, so this 50% is not a joke, it's a different story if crushing blow damage is mitigated by defend first then its damage is multiplied by 2.
Being the slowest weapon is not always the worst thing, it has its advantage if you know how to exploit it.
That being said, i consider hammer, axe and spear being equal, my only disappointment is sword, its counter is easily negated by other weapon.