This didn't age well. Like I said, it's way too early to pick who would win the game based on performance. You saw how Leverkusen played in their first games, they were dominant as usual but they almost shared the points if they had not gotten that late goal to win the game, how does that convince you that they will finish the season unbeaten? Bayern Munich also finished won their game the same way.
Leverkusen's loss to Leipzig doesn't mean they won't compete for the league this season, its just the second league match of the season, there are still 35 matches to play.
If you are talking about dominance in the game, then remember the season that preceded the one in which Bayer became champions, the one when they were at the bottom of the table for a long time, simply because they could not score, although they played very well. Leipzig is a strong team, there is no doubt about it, but Bayer should have played better at home as champions, maybe one defeat is not a death sentence, but now in case of Bayern winning they will be in the role of catch-up, and for Bayern this can be an additional incentive.