+atk/-res Sakura worth investing?

Having an offensive healer is great, even more so now because of Refinement and the buff to staves. The staves at + now heal based off of attack, so having an offensive healer pays off more for actually healing.

I would recommend Wrathful Staff as the B slot, but you don't have Genny it seems? Dazzling Staff refinement is a lot better for the healer, even if they have a low Atk stat. Beyond that I'm not sure what to use as a B slot. A breaker definitely seems like a solid choice due to the lower speed of Sakura.

43 Atk with Fear+ is nice but, the speed is a concern, you don't want her to get countered or doubled, she's kinda squishy. Dazzling can fix that a bit.

Because of Sakuras lower speed I'd make her more of a debuffer then a damage dealer. I would suggest to add to Fear+ by using Speed Smoke for C slot but that's not easy to come by, I don't even have a Sigurd. Either an ally buff passive or threaten speed. And work on the seal from there. Team up with a dancer to either save or ensure kills with Sakura.

it helps yes

wrathful Sakura works because she doesn't NEED dazzling ,and she can take a hit from those with DC

give her Quick Riposte or Bow/Swordbreaker for the B slot, or Wings of Mercy if you're feeling spicy with positioning