The health regen isn't easy to access. It's the last skill unlocked in the subclass and removes your ability to turn invisible or extend the length of blade dancer.
It doesn't heal you fully, it just gives you a bit of health and begins shield regeneration. If you're shooting at the BD when he activates it, he gets nothing because you're stopping the regen instantly.
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If you don't have your subclass tree fully unlocked you're doing something wrong lol. And go shoot at a BD with any auto rifle in crucible, your words vs the game don't add up haha I hear what you're saying but it isn't exactly like that