does 'S' class ninja means that their Sannins??(Which mean, the three) Because Zabuza was also a 'S' ninja.

I think 'S' is probably for Super. That means, they're very very deadly. That is all.
--------------------------------------

And Hinata kicking Sakura's ass?? I doubt it. I wouldn't go to as far thinking Sakura would lose to Hinata hands down. Probably be a fair fight. Although we've never seen them fight, but Hinata was a pushover compared to Neji and her younger sister Hanabi is better than her, so much so she's look down upon. Same as we look down upon Sakura.