I believe PSG is an overall better team than Dortmund and should easily win over them. PSG are the top team in Ligue 1, they has defeated Barcelona in the quaterfinals, which is a second team on La Liga. While Dortmund is the 5th team on Bundesliga who defeated Atletico Madrid which is the 4th team in La liga. Every stats shows Dortmund have an easier path to semifinals.
It no longer matters where they are in their own league, because all four teams are competing to be the best in Europe. Dortmund emerged as the group leader from the so-called group of death. They may not be having a good season in the Bundesliga, but it is obvious that they are preparing for the UCL with a different concentration. They will have 2 great matches against Paris Saint Germain. We should enjoy watching these.
On paper, PSG might look better than Borussia Dortmund because PSG does have a better composition of players but that doesn't mean that they will be able to win easily against Dortmund because teams from the Bundesliga will always have their own motivation when competing in the Champions League and usually they will be very tough opponents. PSG could indeed get rid of Barcelona, but I think they got it after Barcelona made a very stupid mistake. If Barcelona had played with 11 men in that second leg, I don't think PSG would have been able to win against them.