This is not exactly true though. You can kill a cyclops with the same tactics used for a hydra, sure. But the reverse is not really true. You can get away with so many things on a cyclops that a hydra will absolutely demolish you for.However, the tactic to kill one it's exactly the same... but grindier... more shots to open the heart, more shots to exert it, you get the point. And the damage dealt by H doesnt matter if one is able to cold orbit and can aim steadily.
The damage done is also highly relevant because only a handful of pilots at most have the skill to cold orbit well enough and consistently enough to not take any damage at all. In fact, 100% hydra without repairs has been completed by exactly two pilots.