Thats as sad as they come. Everyone has potential. But not everyone has the same abilities. Relaxed form may help, if your too tense then it goes to shit.
as for improving the effectiveness of the kick to the thigh, try the small "step in" to place the lead foot in the position for a good pivot, and by default your body already has momentum building as it follows through behind the step in. grinding a flat foot wont be as effective.
probably one of the biggest thing that peoplle don't realize about a good round house kick is it come froms the hips and the hipe flexors and if you have tight hip flexors following through with a round house will just feel weird. This is the key to a good powerful follow through round house. Most peope don't actually notice it until they do a art like Muay Tai kicks since most other arts don't follow all the way through so you never notice.