Chelsea has better chance of winning Dortmund, no matter that Chelsea has been messing up before the world cup break doesn't mean you should underestimate them. When it comes to Champions league,they take their matches serious because there is a target which is the cup.
EPL is different from the UCL, EPL is one of the most toughest league that a player needs strength and stamina to survive, Dortmund is a different club which don't play the English style of football. UCL is more bigger than EPL and clubs performance in their various league should not be used to judge the UCL games
Judging from the quality of the domestic leagues of the two teams, not underestimating my Bundesliga then I totally agree that Chelsea is probably better prepared than Borussia Dortmund. Yes, sometimes we cannot deny that the competitive differences of a league will affect teams participating in bigger competitions like the Champions League like this. Paris Saint Germain is the picture I will give when talking about this, what is Paris Saint Germain lacking? they have everything, even they are inhabited by star players, but in the Champions League, they can't do more to compete with other teams.
EPL is the toughest of all the Europe leagues. That's why you see clubs in the EPL table who are already close to the relegation zone end up winning clubs in the top four tables of other leagues like Italy, Germany and France.
If u browse the result of the Europa matches played by England clubs like westham, Bournemouth, Brentford, Aston villa and many other England clubs who haven't crossed the EPL top-4 table for the past 7 years, you will understand that EPL is very tough. For that, one wouldn't underrate any England team in any Europe competition.