Hydra is an interesting unit to play with in single player. It's tanky and has an AOE attack - good features to take care of unsupported blobs in AI armies. Hydra was supposed to fill the same role in multiplayer, but for that it's too slow and too vulnerable to anti-large ranged units. The same problems that plague other anti-infantry monsters. Probably a straight forward fix would be to give the Hydra physical resistance and maybe a silver shield to block ranged fire. This way archers won't be able to kill it in seconds, another solution can be a speed buff to 50 or so, like the tomb scorpion's speed. This way the dark elf monster can get to the fighting faster and do it's job.
But i was thinking of a different way to make this unit a desired choice for dark elf players in online. Since it already has a form of a ranged attack as it's ability. Could a complete role switch be made by making hydra a specialist artillery unit, similar to Cygor.
Considering how powerful it's fire breath is the firing rate and accuracy can be taken from the Cygor. Witch I think is in a very good place after the last patch - not too accurate and not too inaccurate. And the ranged can be lowered to 255, like that of the ushabti. So the Hydra won't feel like complete copy of the Cygor as far as functionality goes.
My proposed idea is to create a unit that would give the High Elf roster new tools - tanky monster artillery that can damage at range, but can also be used in melee if necessary. In the artillery role it's slow speed is no longer a huge problem like before because it has a ranged attack, even if it's only 255 units. And at that range it's fire breath can have the same spread as the casket of souls and the same damage per single "fire ball". I don't have access to all the numbers so actual stats of the "close range artillery Hydra" are up to different people to decide.
The idea is to make Hydra useful by repurposing it from a failed melee anti-infantry monster unit to something that ushabti are right now. An intermediate range monster that's good at ranged attacks and has melee stats good enough to protect itself from flanking cavalry and be used as support melee unit. I think CA created an interesting unit niche with ushabti that can be applied to other units and broadening the available Dark Elf arsenal, for example.