That's only partially true. The betting odds and lines are not there to predict a winner - they are there to try and get equal money on each side of the table. More often than not, the end result is that it is pretty accurate, but that's largely due to wisdom of crowds. Predicting winners is not goal of the people who set the lines.
As for the other comment, no team in any sport will be overwhelming favorites to win at the beginning of the season, due to the vagaries of small sample sizes.
Picking the Phillies to make the playoffs in Major League Baseball is a safe bet - after 162 games, generally talent wins out (they are -300 to win their division). But give them three additional playoffs series after that, each of which is a race to four games, and luck plays a much larger role (+200 to win the World Series). The NFL is even more difficult (New England +500) because the season itself is so short that luck plays a much bigger role all year long.