Of course they don't have the consistency. Their squad is simply not comparable to Bayern's who even with half of their team injured can field the strongest starting lineup in the entire league.
Which makes me ask why Dortmund are actually expected to challenge Bayern for the title? Even with today's loss against Cologne they've got 38 points after 17 matchdays, which is a points tally Klopp's Dortmund only surpassed once and is normally enough to be top of the league. With Bayern gifted penalties left and right and Dortmund getting screwed a few times I'd say that's not bad at all.
The way Bayern have destroyed the league by buying out the competition, it will take a much longer time to break this stranglehold. Let's also not forget Dortmund had 23 points less last year at this stage. Barring a meltdown in the second half of the season, they'll comfortably reach the Champions League. Maybe then they can strengthen the squad and mount a proper challenge.