It's not like bruisers = autowin. You can beat them with great teamwork. However, if you don't pick bruiser team, then you are the one, who needs to make up good tactic, you are the one who needs proper positioning, you are the one who needs to play super carefuly during entire game.
Meanwhile, some Darius or Singed just midnlessly rolls his face over keyboard with 0 effort, 0 tactic, 0 positioning and... he wins most of the matches by doing that.
High risk low reward vs low risk high reward.