The only thing I’d experiment with on the kite would be to slow down the motor which might reduce some of the wiggle.
I used to fly kites like this as a kid, and we had to tie a bow string on the horizontal cross piece or the kite would shake side to side like crazy, become unstable & crash. Also, too short on the tail = crash. Too long a tail = too heavy & kite won’t lift it in the light winds we had in Phoenix. The goal being to get to the end of all the string you had.