Does hydra cause balance issues?
Seriously, it's a single item which gives AD melee champions the ability to wave clear, a naturally mage ability, and better sustain than just about any mage.
The amount of utility and stats that hydra (both forms) provide is undeniably the best most from a single item in the game. Though it's build path is pretty easy without any kind of massive gold gaps. Though just in case it did need, say a BF sword, tiamat increases your farming power.