1-I never said he got killed by a rasengan either xd but the third's fighting style was nintaijutsu where he utilized ninjutsu within his taijutsu fighting style. The 3rd Raikage would of had to use long range ninjutsu (which until stated otherwise he doesn't have) in order to beat Sage Mode Naruto.Oh really? It'd be nice if you can post the pages which state Kabuto has full knowledge on all his summon's abilities.
I never said he got killed by a Rasengan. I said he failed to dodge/overcome that jutsu.
Zabuza only used his hidden mist jutsu. His fighting style is based around this one jutsu and silent killing. You're suggesting that instead of having an Edo Itachi spam Susano'o, he'd make him use bunshin feints and finger genjutsu all day long.
2-I'm not suggesting anything that kabuto would do. I'm not Kishimoto so don't ask me what kishimoto would do. Needless to say I'm only proving that they retain their unique fighting style. 3RD raikage is also another prime example, along with Pakura and that magnet user that can attract anyone who touches his shurrikens.