the reason why han is in move 1 is because you want to clear all the buffs asap.

the whole point of the team is to endure up to round 6+ while stacking roshi's defense.

You win the fight by killing your enemies with poison and ignition or, eventually, by owning more hp at the end of round 10.

You are not supposed to fire roshi immediately at the beginning of round 2, but after sakura standard attack landed to add another stack of poison, so that is move 1 or 2 doesn't matter much (you only want to use roshi soon in round 2 if the enemy lineup is able to kill one of your ninjas with the barrier up but is not without the barrier).

Roshi may be interrupted? yes, but is not an issue. You want him to stack, so if gets interrupted by a long combo chase triggered by the interrupting effect is fine.

the best distributions on the field for them are:

Sakura x x

AF x Han

x Roshi x

or

x Roshi x

AF x Han

Sakura x x

right now the lineup works only in the healing tip version with giant katsuyu summon mystery rank 3, but requires you to wisely use your healings.

the neurotoxin version is not anymore competitive.

P.S. if you are against a heavy ignition enemy you are doomed regardless, the same if you can't endure hits with your sakura, so there's no point in hiding her behind other ninjas.