I'm a group fitness instructor (aerobics instructor) & have taught cardio KB as well as boxing with hitting gloves & bags.
I find cardio KB to be a good workout AS LONG AS we move & shuffle & kick a lot.  Just punching air doesn't get my HR up much, but mixing it all up, it IS a good cardio workout & can be fun.  However, after wearing gloves & really hitting & kicking bags - I hate punching just air & it feels like nothing.  
I also find cardio KB to get boring after about 20 minutes, b/c there's less of a variety of moves to work with relative to step aerobics & regular hi-lo/floor aerobics.  
Additionally, no matter how much I cue & cue & give examples & demonstrate, most ladies STILL throw their arms into the air & flail about 

  Most frustrating for me - thinking of their poor joints!!!  It looks hideous too!  Keep your movements tight & controlled!
Taking up real martial arts is a great idea as well!
As far as "taking weight off" - studies show that as far as working your cardio vascular system, 
 it doesn't matter what you do.   If your HR is elevated to 70% of your heart rate reserve for a solid 45 minutes, it makes no difference if you're biking, running, kicking, dancing.... so do whatever you find the least boring.