I'm running these two myself, and I can confirm-- it's absurd.
For those unaware, Nino naturally gets the powerful Gronnblade tome that makes her deal extra damage for every buff she receives, and Eirika is uniquely capable of passively giving allies two buffs at once thanks to the effect of her unique weapon, Sieglinde. Have Eirika buff Nino's already high speed and attack stats and you have a monster of a unit capable of double attacking most of the cast with criminal amounts of damage behind each hit.
Nino has always been my girl since the beginning, and when I got Eirika...yeah, she makes a perfect partner for Nino. They just rekt everything together.
Nino's attack get stronger the more buff she's getting, and not to mention her already high attack and speed status. Also they looks super cute here, like sisters. <3
As suggested in a previous comic, it's WAY more powerful when you cannibalize Nino to someone else who can use the Gronnblade tome. In particular, if you can pass it to a cavalry or flier (which would mean Spring Camilla in this case) unit, then those "Fortify Cavalry/Flier" and "Hone Cavalry/Flier" skills become game-breakers. A potential +30 Atk and +6 to all other stats if you lay both on a Gronnblade user. Beyond that, just inherit Reposition and Swap onto your buffers to keep your nuke out of harm's way as you delete one enemy per round.
As suggested in a previous comic, it's WAY more powerful when you cannibalize Nino to someone else who can use the Gronnblade tome. In particular, if you can pass it to a cavalry or flier (which would mean Spring Camilla in this case) unit, then those "Fortify Cavalry/Flier" and "Hone Cavalry/Flier" skills become game-breakers. A potential +30 Atk and +6 to all other stats if you lay both on a Gronnblade user. Beyond that, just inherit Reposition and Swap onto your buffers to keep your nuke out of harm's way as you delete one enemy per round.
I see Nino as a speedy and easy-to-use Gronnblade user that needs few buffs to double and kill most units, while Cecilia (the only green tome cavalry unit atm) and Spring Camilla are the powerful and team-specific Gronnblade users that rely on the buffs unique to their own type to kill everything in one hit. Nino doesn't need a lot of skill inheriting (aside from Desperation and maybe Fury) and fits into most party compositions, Cecilia and Spring Camilla reward all your skill inheriting and team building with easy-to-use murder machines, and all three are extremely capable of slaughtering everyone in sight. Saying that it's "WAY more powerful" to cannibalize Nino for a Cavalry/Flier team is an overstatement.
I see Nino as a speedy and easy-to-use Gronnblade user that needs few buffs to double and kill most units, while Cecilia (the only green tome cavalry unit atm) and Spring Camilla are the powerful and team-specific Gronnblade users that rely on the buffs unique to their own type to kill everything in one hit. Nino doesn't need a lot of skill inheriting (aside from Desperation and maybe Fury) and fits into most party compositions, Cecilia and Spring Camilla reward all your skill inheriting and team building with easy-to-use murder machines, and all three are extremely capable of slaughtering everyone in sight. Saying that it's "WAY more powerful" to cannibalize Nino for a Cavalry/Flier team is an overstatement.
Except "taking a slightly more specific setup to use" doesn't in any way diminish the statement "WAY more powerful". Nino is powerful, but Cecilia and Spring Camilla are game-breakingly powerful. This strip talks about how powerful a +10 damage buff is, which makes her capable of one-shotting low-res blues, or single attacks taking out most blues if she gets a follow-up. +30 damage (which is mid-70s attack power before even trying to add anything else into the mix, by the way - and min/maxers can get it up to mid-80s), then Cecilia and Camilla will one-shot anything but high-res reds. According to theory crafters, Spring Camilla with that kind of build can beat nearly every unit in the game but Sanaki, and Cecilia can one-shot even the majority of reds. That's before you even start including anything about any other units in your party besides having fortify and hone. (And really, why wouldn't you want them? They're great skills no matter the build.)
And there's a blarblade, too, if you want to cannibalize Odin for someone like Ursula, Olwen, or Reinhardt. (But why bother taking away Dire Thunder from the siblings, especially when the same ATK/SPD buff makes that double attack a murder machine, as well?) Plus, even a red like Leo can apparently use Gronnblade thanks to an oversight, although that may have been patched by now... But Tharja has raudrblade, anyway. Both Odin and Nino are among the most common drops, at that, so there's little worry of losing out on a chance to use either one on their own... Although Odin is so weak he NEEDS Blarblade abuse to even be viable.
I also frankly find the real overstatement to be that there is that much difference in difficulty to using Nino versus any other potential *blade user, barring needing the 100/300 extra SP it takes to get Gronnblade instead of a different weapon, or the use of the potent movement-type specific buffs versus the general buffs. Buffs in general aren't that common, and if you're going to go out of your way to use Eirika just because you want her ATK and SPD buff, how is that so different from going out of your way to use Gunter for his stronger ATK and SPD buff? During this special quest set that demands all fliers, if you have Caeda and Calla, and AREN'T using their Fortify and Goad Fliers abilities, you're just making things harder on yourself for no reason.
Basically, there's very little cost to using this setup, since burning some Odins and Ninos is practically necessary if you're going to keep slots open in your barracks. (I've gotten 6 Ninos, although that's still not as bad as the 8 Raighs.) Spring Camilla probably loses more, since you're probably shoveling a 3/4 star weapon onto someone who's by definition a 5 star, but the 4 HP per hit isn't necessarily as valuable as the +10/16/28 damage. Cecilia gains +1 damage even before the buffing, and she only loses advantage versus greys, which isn't going to get her the one-hit-kills against Takumi she'd need to be viable on its own. Ursula would only lose out if you were facing cavalry units you would otherwise be able to one-shot, which is a rather narrow set of circumstances, especially in the arena, where cav teams are strangely quite rare.
That said, there is a single reason why I totally understand nobody uses fliers except Camilla, and that's the prevalence of bows, and particularly Takumi. Having a roughly 80% chance of seeing someone who deals instagib damage to your entire party is very likely the reason why they had to create two whole events just to get people to use fliers at all.
