Kiara’s class advantage application is second only to Rulers. Since both Ana and Kiara have offensive applications to their deck for being secondary attackers, Kiara is far better supporting art teams against Calvary enemies(not including Assassins), and Ana is far better against Knights. It’s a tradeoff that’s more in Kiara’s favor. Against an Foreinger, she’s great. Pit either against an Avenger and beast, and Kiara’s superior attack stat and 1.0x damage modifier as opposed to the 9.0 on Casters. The damage sacrifice is far less.
While your NP refund and slightly easier arts chain argument is relevant and something I didn’t consider, there’s more to Kiara’s advantages I didn’t list. She can easily NP twice in a row with her third skill if you’re going for DPS over defense (and if the lack of invul is a problem for her its worse for Ana, whom has no hard defense and doesn’t have the option). Kiara’s heal is notable, especially with its abusability with black grail(less relevant for 3T farming, but great for harder nodes) and her damage reduction against humanoids.
She has AOE stalling potential that’s not reliant on her debuff resist down unlike Ana, whom has a stronger effect (stun), but only on one target, and a 70% success rate on its own, meaning her stall potential is far worse in a multiple boss scenario. They have the same cooldown as well, and the advantage of NP drain is that, after stalling the first NP wave, should you survive it(which Kiara can do), it can actually be used to stall the second one, unlike stun, which would have to be used just before the NP.
The script flips when it comes to their def/attack debuffs/buffs. 40% is better party wide is better than 30% party wide (and more frequent for Ana), but using Kiara’s 1st skill alongside other arts attacks results in a 1-turn application of 69% extra damage against a boss, and 30% extra arts NP refund. This + the previous paragraph is actually why I consider Kiara to be the better when it comes to arts teams specifically.
CasGil is the inferior farmer, yes, but that’s why I was talking in the context of general support. I have to ask how the comparison of Shuten and Ana is superficial? Both focus on enabling the entire party to deal extra damage to anyone (hence why individuals are considering Ana to be a generic support) Shuten is better at this when her 1st skill is up in combination with her 2nd skill and NP. Ana is better in the 2 turn gap between the 2. Both have AOE skill seal. Both debuff attack (Ana does so better at 20% as opposed to 10%). Both have stun/charm potential. Ana is single target, and 10% more chance provided she’s not using her 1st skill for herself, and Shuten has equal chance on an entire enemy party if she waits until after her NP.
What Shuten has that Ana doesn’t that’s relevant (lol NP damage down) is crit chance down, which, even at such a low value, is relevant. Most enemies are 10-20% crit chance. 10% debuff resist down for 3 turns can help seal the deal for servant with an already high-chance debuff. What Ana has is a single-target debuff resist down that lasts for 1 turn, but guarantees debuffs effectively+givers her ignore invincible, and she has a battery. There’s a lot more overlap than you think.
You can point out the arts chains and the battery, but then I can point out that Shuten does a lot more damage despite Assasins and Casters both having .9x damage. Seriously, Shuten at NP1 outperforms Ana at NP2. The battery isn’t the end all be all. Ana is the type that can independently 1-turn NP with a 50% charge. The flip side is that she’s the type that might be good against a mid-wave. Shuten’s the type you’d put on the front line with Kaleidascope with NP charging support, but she’d make sure even tougher non-boss Riders are dead.