Probably the worst part of taking dance lessons is the initial fear of getting started. Then once you start expecting too much too soon. Practice, practice, practice makes for good progression, even if you have no dance partner to practice with i.e. doing the patterns solo. You could spend 50 hours on practicing rumba's cuban motion in the box step (once you get the jest of it from an instructor) and then soon thereafter incorporate it into the rest of the rumba patterns you've learned. Then the hip motion would come easier to learn in the merengue, cha cha, salsa, & bachata.
The worst part of being a dancer is not enjoying ballroom dancing to the fullest... with the progressions you've made. They'll always be better dancers than you at whatever level dancer you become and it can be easy to be dis-content / envious of others. Enjoy the moments and be thankful for them all.