I was rereading the topic and I saw some discussions about Sasori
There is few translations:
So even if it's ambigous. Sasori still has better portrayal than Deidara:
Sasori captured/defeated a stronger Kazekage than Deidara.
Despite his arrogant attitude, Deidara refers to Sasori as "Master," which backs up his earlier claim of inferiority.
Sasori has the hype of defeating an entire nation.
And Deidara admitted inferiority (!?)
Trumpcard=C4 Karura and that jutsu doesn't work against Sasori since he is a puppet that doesn't breath.
Iron Sand could block all of Deidara's explosives except for C0 (draw if Deidara uses that). Gaara's sand blocked C3 and Iron Sand was stated to be superior (Satetsu is the ultimate weapons of the strongest Kazekage, Sasori's tool).
Sasori's puppets can fly, which reduces Deidara's ability to keep distance, and lets Sasori reach Deidara while he's airborne.
Iron Sand projectiles could also snipe Deidara out of the sky with their speed, and one scratch is all it takes for Sasori to win.
Satetsu Kaihō is just one shot.
And if Sasori is going to land a hit/scratch (from any weapon) on Deidara; then, it's over with poison. Sasori has the offensive capabilities to threaten a flying Deidara and the defensive capabilities to block his explosions. Sasori is clearly the superior of the two (except for the speed of his bird, Deidara has nothing defensively).
Sasori has very good feats (it's not pathetic at all), it's just that he has a less destructive fighting style than Deidara. If he loses against Sakura/Chiyo it is because he let Chiyo take the last blow as you said, because Sakura had several antidotes and because Chiyo has infinite experience in Kugutsu and she knows Sasori very well (I would even add that fighting in a cave with a closed ceiling, prevents the puppet of the third to express herself at full power. Sasori could use the Satetsu to steal himself).
I would also add that we are far from having seen all his arsenal: he has 298 puppets, we saw just over 100 of them, and he also has unused rolls.
Killed strongest Kazekage when he was a teen. Used that Kazekage in fight, all his weapons are imbibed by mortal poison... And he let Chiyo kill him,
Chiyo who knows everything about himself and has an infinite experience. Add to that Sakura, his strength and those antidotes.
And Chiyo is far from being weak, she is at least low Kage level.
Kakuzu is weaker. He is tough with his hearts, experienced and uses basic elementary attacks.
I don't think it's as good as Sasori (in fight, Iron Sand can block all Kakuzu attacks). Also, Kakuzu surviving Hashirama doesn't prove anything. We all know that Shodaime can zero diff Kakuzu. IMO he must have spared Kakuzu because of Shodaime's kindness.
Alongside Kisame and Deidara, Kakuzu represent mid Akatsuki level (mid Kage). Sasori is above that. He is more like an Orochimaru without ET (was his teammate, and I find a lot of similarity between them). IMHO Sasori is between the mid Akatsuki level and the Dojutsu trio. He is underestimated because his fighting style is not flashy like Deidara's, because he died first at the very beginning of Shippuden and against Sakura/Chiyo.
The only true difficulty for Sasori in a fight against Kakuzu will be to destroy the doton heart.
Hidan is dumb, the slowest of Akatsuki in attack
He only showed his ritual (not necessarily obvious to set up 1 vs 1). Too bad with his immortality and his god Jashin, there was potential.