The girl in Oresama Teacher is smart WHILE FIGHTING. And that's it. Otherwise, yeah, she's pretty ditsy. I don't know if I'd say straight up stupid, but she's a smart fighter, outside of a fight, she's better relying on the judgement of others.

Also, my suggestion would be Akagami no Shirayukihime Lead female is a healer who stands up to her oppressors and is an equal with her love interest as far as personality goes.

Warau Kanoko-sama
Last Game
Seol Hui
Ciel - The Last Autumn Story
Lady Detective
Pellua Iyagi
Romance Papa
Yume no Shizuku, Ougon no Torikago

“The mind is its own place, and in itself can make a heaven of hell, a hell of heaven..”
― John Milton, Paradise Lost

Smart female lead shoujo manga

kanoko from warau kanoko sama and koi dano ai dano (the sequel)

You should really read, “ I reincarnated into an prime game as a villainess with only destructive flags”.
It’s really good and worthwhile, it’s on going, you can read it on manga rock ( a great manga app)

Okitegami Kyoko no Biboroku should be the one.

Kisshou Tennyo - a femme fatale story; really interesting as it explores gender roles and the hardship experienced by females

Akatsuki no Yona - starts out a pampered princess but progressively becomes emotionally-strong and uses her femininity to her advantage (she knows she's not physically strong but has other strengths)

Cat Street - finds her own path

Anime/Mangas w/ smart female tacticians:
Song of the Long March
Katanagatari

Cunning female chars:
My Secret Brother
They Say I Was Born a King's Daughter