Ibuki has high attack - the highest for her class - while being basically the worst in terms of HP. She has 4 passives but only 1 is that great - Dragon Kin EX is a 12% Buster and a 200 Damage Cut. She’s got a Divinity variant that gives a flat 250 attack bonus and increases her buff removal by a little, then Riding and Magic Resistance which are normal for Sabers (do more Sabers have Riding than Riders do? I’m actually curious. )
Her 3rd Append is anti-Ruler. They aren’t that common an enemy to find and they’ll still resist her damage anyway.
S1 is a large NP battery - finally, we have a Saber that actually has 50%. Mordred and OG Saber had 30% ones that could add up to 50% (or more) after their NP, Suzuka had 50% but spread out over multiple turns, and then there are a few like Jason that can NP refund enough that they don’t need a full battery, but this is the first AoE with it just actually there, ready to use. It also has a 3-time 40% Attack buff - great for farming or Buster Brave chains.
S2 is a 3-turn Buster increase (30%), 3-turn Defense buff (30%), and a 1-time star bomb (20) on a nice and short 5-turn CD. As Ibuki is a Buster gorilla, and she already has a pretty good passive that gives her more Buster and defense, this skill adds to her kit nicely. The crit stars also help with her s3.
Said s3 is a ST NP Seal (very nice skill), 3-turn Crit damage buff (50%), and 3-turn Special Attack vs. “Undead”. NP Seal is always a nice skill to have, and the stars/Buster buff from her s2 go nicely with her crit damage here - she doesn’t have any weigh to change her star weight, and as a Saber it’s pretty middle-of-the-road, but if you run her with Casters as support she should still pick up most of them herself. Undead isn’t a very large enemy group though: Ghosts, Ghouls, Skeletons, Scarecrows, Zombies. The Black Samurai that show up in Shimousa and the Dark Shinsengumi from our last Guda Guda also are Undead. Skeletons, Zombies, and Ghouls looked like the only ones she’d have class advantage against (Ghouls are usually Berserkers, while Skeletons and Zombies can be most classes.)
@Cards covered her NP damage pretty well in his thread linked above, and how it compares to OG Saber, Altera, and Muramasa. Going into it briefly again here, it’s an AoE Buster that pre-casts a 1-turn Ignore Invincible and then a post-damage Buster Resist down based on overcharge (20%—>40% @max OC). It also Ignores Defense so it can be useful for some harder fights.
For damage, she hits 28.4k—>47.2k without Undead and 42.5k—>70.7k with that. That puts her well behind OG Saber (38.8k—>58.2k on her NP) but mostly ahead of other AoE options like Quick Summer Okitan (27.0k—>45.0k), Arts Saber Shiki (29.5k—>44.2k), or 4* Buster Saber Alter (29.3k—>42.3k). Again, Cards put more details on some of this in his thread that does more work than I do by including their damage numbers with optimal supports, which would allow her to out damage OG Saber by anywhere from 100k—>250k @NP5, depending on if it’s anti-Undead or not.
When she released, I remember thinking I liked her more for challenging content than farming - really, a lot of CQs from events are boss rushes in one form or another, so AoE is actually pretty helpful, while having tools like a passive damage cut (stacks with someone like Waver or Reines), her own Defense buff (also stacks with Waver or Reines), high attack and crit damage, and Ignore Invincible/Ignore Defense that are probably going to see use.
For instance, in the Imaginary Scramble event CQ, we had Gilles and many different Jeannes as backup. While ofc Ibuki would have struggled vs. Archer Jeanne, she is AoE and would have class advantage vs. Summer Jalter + Santa Jalter, been neutral vs. Gilles/Lakshmi Bai/Jalter, had at least some extra damage via 3rd append vs. Jeanne, been able to get around the taunt thrown on Gilles due to being AoE, sealed Jalter’s NP that would pierce any Invincibility skills you had, and been able to get around either Jalter’s Invincible skill or Jeanne’s NP-based Invincible to guarantee damage.
But when it comes to farming, I’m not as impressed. She can work, of course, even now, the way any 50% self-charger can. And her damage is going to be pretty good. But if you already have a built OG Saber, she works just as well for that currently. I’m always hesitant to summon a servant just because they could have greater performance in the future if I could summon someone else for them. FGO gacha is harsh, and if you bank on using her + double Koyanskaya but then you fail to get Koyanskaya, she’s just a side grade to Artoria.
But check out the first linked thread for what she can do with support, as it does make a big difference to her potential.