I did this because you would be BloodBending when it isn't a full moon, which if possible would cause immense strain to your mind and body. That's also why the damage doesn't happen during a full moon, which correlates to the show. Also, I know about Yakone, he is an exception with some strange genetic mutation. BloodBending shouldn't be limited to only a full moon so ppl will be abe to any time anyways. This is also why the power of it changes depending on the moon phase.
No, I think that heart loss is the way to go. It's the best way to 'limit' bloodbending and make it not op. The heart loss imitates strain on the body, which is why after taking a certain amount of hearts (strain on body) you can no longer do it. Next, I talked about Yakone in my above response. I do think that only BloodBenders should be able to escape being BloodBent while the other bender can still BloodBend you, possibly only by using your BloodBending to negate theirs.