Dortmund did not manage to get a win in their friendly game against valencia, and they lost with such a large score 3 1 and they only managed to score from the penalty spot, its not looking good for dortmund i guess we will see bayern a champion once again.
You shouldn't take friendlies too seriously. Of course, the score is important, but it should not be forgotten that there are matches to try whether the team is ready or not. So even though they lost 3-1 to Valencia, it's too early to say it's over for Borussia. Bayern Munich will most likely be champions as always, but Dortmund will do their best.
Same remark, friendlies in general are used to test the players, how ready they are, testing some tactics, positions for the players, substitutes...etc
Even players won't give 100% of their efforts there, otherwise ManU for example wouldn't score 4 goals vs Liverpool!
Bayern will experience a change with their new attack line so a drop will be expected especially in the first weeks. It is an opportunity for Dortmund and the others to challenge them for the first place!