Not necessarily. This is technically more based off the FFQ mechanic than anything else, with a slight nerf by forcing the spawns to have at least one Hydra there to survive. I considered the problem of different Hydras spawning the same heads, but keep in mind that there are other creature spawning cards without the limitation of death. Once you kill a Hydra, it's heads will "magically" reattach to another one. If you kill that one, then everything dies because there is no more hydra to target. As for mutation, that could possibly be dealt with in the same vein with a mutated Malignant Cell, possbily give a carryover passive "Lifelink" ability that forces the mutant to rely on the Hydra anyway. Also the sheer power of the Hydra's ability is compensated by heavy cost and the need to use quanta to respawn heads. What I am trying to say is that technically, the Hydra and the Hydra Head are two seperate creatures, rather than one split across two cards. Hydra Heads could be played like "bombs" as Kuraitou mentioned earlier, then dying, possibly for the benefit of a Bonyard or Soul Catchter. They can also be played to support a Lobo'd/Frozen/Delayed Hydra. The pair's greatest weakness is actually Mutation : if all the Hydra become mutants, then all their heads die.
That being said, I appreciate the criticism as well as the addition of my ideas to the crucible.