Parker plays a lot harder in the regular season than Rondo. Especially when Rondo is playing hurt like he was for weeks before he tore his ACL.
Rondo's style of play is meant for the playoffs. Despite being so quick, Rondo is more of a half-court play-execution PG. He rarely plays off-the-ball.
Especially in the regular season, Rondo generally prefers a slow pace. In the playoffs, Rondo's ball domination pays off because he becomes more aggressive in every facet.
Pierce suffers from a similar syndrome. Pierce is 100% mentally there, but until the postseason, he physically can't execute the defense and lift until his juices are flowing.
Rondo doesn't need to play more like anybody.