I think Dortmund will definitely not be the favorite. I don't think they can win this match.
As you said, their Champions League performance is not that bad, but they are playing really bad in the Bundesliga and not many people like this team this year. Their opponent is a very fit team, they have the motivation to win this match. That's why I think Dortmund will lose the next match
If we talk about both teams in their respective leagues, Sporting can be said to be more favored in the match against Dortmund later because if we look at the performance and also the position of both teams in the standings of their respective leagues, the difference between the two teams is very obvious. However, in the Champions League anything can happen because this is a very prestigious league of all leagues and of course all teams will focus and try their best to be able to perform well in every match, and I don't see Dortmund being too bad throughout the Champions League and of course this will be a life and death match for both teams to be able to qualify for the next round.
After the exit of Amorim Sporting CP having huge decline into their performance specially they fail to win any game in Champions League with their performance is also not stable in Portuguese Super League even they are having good comeback and took top spot, but their performance in Champions League is surely going to have big problems for them in game against Borussia Dortmund.
In first leg Sporting, CP is going to play at home which could be beneficial for them but still things could be tricky because Dortmund is well experienced, and they are also having good record in this elite league which give them good advantage but their recent defeat against Stuttgart at home give them setback which needed to be overcome.