He's a good coach and seems like a nice guy, his results are more or less what you can reasonably expect. But it seems like there is just absolutely no way that he can win a title with Dortmund. He's someone who seems to value stability and caution greatly and that just doesn't fit Dortmund or their squad. His tactics are so timid, he barely uses aggressive pressing, the possession play is quite risk averse, too. It's good enough to beat most teams in the league and get a convincing second place, but there are games, where you see that this "let's recycle possession for 50 minutes and see if they make a mistake or get tired eventually doesn't work. Like when they faced Lazio and instead of trying to gain some respect by opening aggressively against a team that hasn't played in the CL for a while and didn't start their season well it was more or less the same slow-paced rhythm as always and soon Lazio were confidently taking charge of the game. The same in the cup against Bremen or at home against Paderborn last season, some teams try to ambush Dortmund early and too often it works, because all they know to do is play it slow and safe, they cede momentum and when the weaker team realizes they can really make something happen that confidence lets them do some heroic stuff.
Away games in Europe:
A scrappy 1-0 win in Brügge and a 2-0 win in Prague and a 2-0 against a Monaco team in relegation form, the rest from 1:3 against Barca, to 0:2 against Inter, to 0:2 against PSG, to 0:2 against Atletico, to 0:3 against Spurs probably not even 1.0 xG between them. Games in Munich fit that list very well, too. It's the easiest football bet in Europe. Always some passive, "safe" approach, little to no pressing, sitting deep, giving the opposition full control only to eventually come to the surprising realization that you can't just defend deep and concede the midfield against these teams or play a toothless possession game for 90 minutes without getting punished eventually.
Sure Favre offes a safe 2nd or maybe 3rd place (if Leipzig do well), but who cares about that, when the squad is good enough to pull off an upset here and there, instead of defaulting every away game against top clubs or dropping in the cup to Bremen. A 6 out of 10 season is not something to hold on to and things would have to go very wrong to drop out of top 4, especially now that Leverkusen have folded.