I think that it doesn't matter if you dance on a slow song or a fast song, but what matters the most is the level of enery. It should be the same throughout the song. If you have eye-catching expressions and an appealing way of performing that particular song, you can definitely get the appreciation from the judges.
As for Hiten-Gauri, Hiten has improved a lot, but I think that Gauri has not yet progressed a lot. She doesn't enjoy the song. May be she is always trying to take care of the perfection in her dance, which is good/bad sometimes. Hiten is a "Happy-go-lucky" kind of person. He performs irrespective of the consequences and even tries to rectify his mistakes. I don't think there are any errors from the choreographer's side. May be he should give HG some dazzling dance steps so that they can grab the attention of the judges.
I love this couple a lot and want them to reach till finals as I think they have a lot of potential. I wish all the best to HG for their next performance 😊