Really? Where's the proof that he could break out of it on his own? Please provide me with some and i'll gladly change my answer. All you're doing is speculating and i don't do that.
if he launched 3 of his most powerful long ranged attacks, Itachi would not have the chakra to walk on water after that, it's like Naruto using 3 Rasenshuriken, Chibaku tensei instantly kills Itachi and Jiraiya, Minato can escape with Ftg, and comeback and hit him pointblank with a Rasengan, and be home in time to check up on his baby boy Naruto