EDIT: WRONG BLOODY MASTERY NAME. I MEANT RUNIC ARMOR.
The mastery is so strong in the jungle right now. Anyone that has an easily accessible heal or shield bypasses any difficulty the jungle has and currently levels of sustain rivaling warwick or fiddlesticks. If it's left as is I worry for the jungle meta.
This allows champions like Rengar and Tryndamere (who were previously thought of as "risky picks") to be very safe and snowball much easier. Champions like Nautilus clear without ease as well.
Meanwhile, picks like Jarvan and Wukong get wrecked without it. Riot, please.