Domestic form means nothing in the CL. Dortmund have been by far the best CL team this year. Years ago when Chelsea were the best team in Europe (era of Drogba, Makelele etc), United beat them in the league, but they had the best team in the world by far in those days, and their European dominance hindered their league form.
Dortmund are putting all their eggs in one basket with the CL imo. Have you seen their matched this year? Breathtakingly good.