Initial Balancing Thoughts - Predator
The cooldown on this particular rune seems extremely hefty, especially compared to other runes. Majority of the others have an immediate impact in the game from level 1, whereas with Predator - while useful in roams and ganks - offers nothing for that. It even requires boots before it can be used, putting aside the immediate cooldown... as a KEYSTONE.
Even when it is used, there is no guaranteed reward in using it. Sure, you can pull off a gank with it, but what if it goes sour? You are without a keystone for the next 150 seconds, give or take, while your competition continues to reap the benefits of their own. I don't even feel like it is particularly worthwhile on Hecarim, who arguably gains the most from it.