Redwizard007
Adventurer
The problem the Frenzy creates is that, if they use it too early in the adventuring day, you're basically weakening the entire party for the rest of the day outside of combat (get it to 3 and its inside of combat, too). Anything you were good at, now you're bad at it. Strongest guy in the party? Not anymore. Agile and unarmoured so stealthy and good at climbing/swimming? Not anymore. Keen senses? Not anymore. Any skills at all? Better off someone uses the Help action on someone else for all those rolls. So you have to hold it back until late in the adventuring day.
I have yet to play a barbarian in 5e so maybe I'm missing something, but isn't that the same thing that would happen to a wizard that used his high level spell slots on trivial encounters, or a paladin that ubersmited a guard instead of the BBEG, or a monk that blew through his ki points, or a sorceror that uses all his metamagic early, or...