Right, but how is it more efficient?
If the hydras spawn inconsistently, then 20% attack speed, +50 HP and 15 Frost Resistance might actually be better and the Hydra spawn will in the end just considered a gimmick.
You know, interesting is not equal to awesome or even useful, and “awesome!” is the feeling you should get when you find certain legendaries (certainly not every single legendary, but some).
But why should anyone do that if magic and rares are on the exact same powerlevel as legendaries? Why should I prefer an inconsistent chance for a proc over a constant and reliable source of damage and defense?
It also gets rid of the whole idea of progression. You find a good magic item (which are fairly common) and then every item you find afterwards is not an upgrade at all, since it is on the exact same powerlevel.
Someone who build his char in the endgame for 6 hours will be as powerful as someone who played his char in the endgame for 300 hours (in regards to itemization), regardless how many legendaries he has.
This is neither interesting nor awesome.