the story line in naruto is WAY better than DBZ so dont bother to compare, the ONLY fight that you can relate to DBZ is the hokage one but thats because there was SOO much more other things going on that it was impossible to focus on it all at once, while in dbz they only have a fight and lengthen it for like 40 eps while nothing else is going on, the charecter developement is insane, they almost focus on it TOO much you basically know the life story of almost every character in the anime whether significant or not. Yes, it has become mainstream, but just because there ARE some portion of the world that are idiots that like it because its action that they compare to dbz doesnt mean its a bad anime. i havent seen samurai shamploo nor samurai 7 (will look into it now) so i cant say anything about it, but im just defending my opinion. also not ALL the fighting is in a dbzesque type way. Take Shikamaru's fight with temari, it was badass not because of action but because of how the fight was planned out and had a use of strategy rather than a dbz (power up and repeat these frames of punches for about 2 mins) type of battle.
OH and also the flashback serves to drive either the story or the supposed "shallowness" you call as backround for the characters
