Real Madrid can be considered superior, based on the last 5 head to head matches between Real Madrid vs Dortmund in the Champions League. However, we must know that Dortmund's last 5 matches recently, Dortmund is very favored with 2 wins in the Champions League and 2 wins in the Bundesliga, and only experienced one defeat in the Bundesliga match.
I think the Champions League Final this time will be very fierce for El-Real, considering that Dortmund's defense is difficult to penetrate and has conceded fewer goals than Real Madrid, and it is very likely that there will be extra rounds, or even a penalty shootout to win.
Don't use last 5 matches to judge Real Madrid performance to judge the final match between them and Dortmund, if I remember correctly Real Madrid has won the Laliga trophy and other matches aren't that too important for them Anymore and because some players has had injuries and weren't fit to play and switched them with other players that weren't too frequent in starting games, so you can see where the draw games came from right.
However, Dortmund is still using their players which will eventually play on that same Saturday, that makes them even vulnerable to loss. Real Madrid will come hard for them and since past years, even at worse of Real Madrid they beat Dortmund many times, this final match isn't exceptional as well.