It's great that you've found a way to make SCA combat more engaging than -- say -- walking a treadmill. It's definitely fun. It's also definitely more activity than you're getting now (sort of by definition... as long as you're adding activity not replacing it).

On the other hand, it's not a replacement for going to the gym, long daily walks, or any other sort of aerobic excercise. I find that SCA combat is a motivator for me to go and do those things, because they'll all improve my fighting (increasing stamina or flexiblity, losing weight, improving core strength all make fighting -- and most of life -- better).