Quick note: Tsunade the 5th hokage is a better option than the Sannin war alternate.

The whole point is to cause huge damage in 3 turns from the Iron Sand World Order and the Sand Hell's Ninjutsu Then poison starts to rack up

That is if you can pull off Iron Sand World Order. Remember that it is not a prompt skill which makes you vulnerable from your opponents CC and you need your puppet alive so you could cast it.

That is true

Before you get to turn 3, most likely you are dead.

Both frontline ninjas are not good at all.

If I may be a little harsh for a moment...

Gaara's and Sasori's mysteries are both ninjutsu based, meaning to say Poison Tai wouldn't help them at all.

Sasori's standard attack with puppet already has poison, so that's another redundancy for Poison Tai.

Sasori's mystery is non-prompt, so I wouldn't count on it being first slot as my combo trigger.

Now if I were to put my touch on this team, it would go something like this:

Water, Gaara, Blank

Tsunade, Sasori, Blank

Blank, Blank, Blank

Talents would be 2 2 2 2 1 Shiba or 2 2 3 2 1 Monkey. The Shiba talents allows me to move Tsunade down 1 grid so that she can share the heat with Sasori if there's an enemy at the bottom row. But if Sasori is disabled, my entire combo chain dies, which is why I thought of the Monkey talents.

So now, the whole idea is that round 1, Gaara breaks auto barriers, while Sasori acts like *l-round tougher version of Kankuro (i.e. 100% combo starter). Round 2, If Sasori c*e his mystery, then great. But most times, I'll be using Water's Great Shark Bomb instead. Round 3 will be either Gaara's mystery or Tsunade + whichever is left between Iron Sand World Order and Great Shark Bomb. From here, I'll try to make sure that every round, I have either Gaara's mystery part 2, Water's mystery or Sasori's mystery to AoE with, even if it means that I have to refrain from throwing out all my available mysteries despite my abundance of chakra.