As long as there is personal opinion there will always be "Heavier" music. People can think of the brutal style of death metal as heavy, a simple thrash anthem from Metallica or Slayer as heavy, an epic melodic power song by say Amon Amarth some would consider very heavy or just simply even earlier stuff like Judas Priest, Iron Maiden, Black Sabbath and the like will be considered heavy. People will always cherish what they really love in their music. "Heavier" music is and always will be opinion differentiating from person to person.