From my experience with Itachi, he's a bit squishy but have some skill set that do wonders if you pair him with the right ninja and main. Let face it, there's a reason why we have 5 different mains, it means we have 5 type of gameplay with different ninja to compliment it. For an example, lets take a look at lightning main, he's a single hitter with vengeance, can interrupt, have skill to 2/4 attack in 1 turn and not to forget; the vampire team it paired lightning main with Guy, so they can double leech hp each turn.

Short story, here's a formation i use using Itachi

Itachi - x - x
Kankuro GNW - Pain Gakido - Earth main
x - x - x

skill 23122 summon dog of hell
have mini combo, ignite/poison, em cleanse+shields and lastly 2nd turn dual aoe from main and kankuro.