Astra is underrated, change my mind.
Astra is underrated in comparison to Dragon Fang in terms of 4 cooldown specials. Many builds use Dragon Fang when Astra is superior. Builds tend to use Dragon Fang when a unit's Atk gets higher and higher, but actually Astra outperforms Dragon Fang the higher one's Atk gets.
Take a neutral Winter Ephraim, for example. (45/57/23/36/29)
The build says to use Dragon Fang. But here, Astra is a very viable option, since it outperforms Dragon Fang up to the foe having 38 Def. And with weapon triangle advantage, it outperforms Dragon Fang up to the foe having about 49 Def. With an Atk boon, it will outperform Dragon Fang up to 40 Def and 52 Def with triangle advantage.
Astra is an absolute monster with triangle advantage. Of course, the flip side is that it is worse with triangle disadvantage. But is it necessary for the unit to break the weapon triangle if the unit is on offense?
Astra is especially amazing on dragons since the damage dealt will scale off the foe's Res, which tends to be lower.
Astra of course has its weaknesses, especially on defense, but overall, it is not as bad as people think. Used correctly, it can destroy many enemies better than Dragon Fang.
Answers
It's always better. You do realize that in all situations where astra deals more damage (which is most of them, yes), both specials will kill but astra will overkill by a LOT.
On the other hand if the foe has ridiculous amount of defenses astra will do nothing and dragon fang may be the only way to kill.
There is one exception, if the foe has ridiculous amounts of hp (eg 99) but normal defenses then astra is better. But abyssal LHB maps are the place in the game where this happens and astra is usually not a good choice because it takes too long to charge. I Have beat a few abyssals using astra on reinhardt though.
PS: Also you do not use either astra or dragon fang on units with low attack, that's just stupid... you're much better off with luna in that case.
Basically, this.
The only time astra beats dragon fang is when enemies have unimposing defense (or res) but tons of HP. 4CD specials tend to get picked for blasting through tough defenses, and astra tends to perform very poorly in those situations.
Or when you want to do over 200 damage for kicks. That's a good use of astra.
