Thats just my opinion though, and I know players have a different range of opinions based on their own expectations and experiences
(If a permanent with a finality counter on it would be put into a graveyard from the battlefield, exile it instead.) At the beginning of your end step, return up to one target enchantment card from your graveyard to the battlefield with a finality counter on it
The ever-looming threat of Gargos, an 8/7 creature, fighting an enemy creature is enough to put off many opponents from targeting your growing army of Hydras
Much of this is down to the imbalance of the early stuff making only the top quality fair things viable for cube use
When your opponent does play a powerful creature, use a removal or counter spell to get it into their graveyard and boom, pay a paltry amount of mana and that puppy rises again, but this time on your side as an unholy abomination of itself
If you face decks with heavy enchantment play, you might find yourself wishing you had a splash of green or white