They both do. A team that wins 6 games in a row in a single elimination tournament is clearly the best in the field.
Likewise, a team in the NHL or NBA that wins 4 best of 7 series in a row is the best in that league.
Your first statement clearly wrong as any team can have an off night in a single elimination tournament. But if they had a 5 or 7 game series they can bounce back and make adjustments.