I am a main barb player I would concentrate changes of barb.
2-Piece Bonus: Double the effectiveness of all Shouts. Feared Enemies take double damage.
All 3 shouts under tactics or just threatening shout? I would suggest all shouts (perhaps this would be way more strong) to gain all ruin effects. Or alternatively gain the base effect of all shouts link Inna?
It also would be pretty hard to link making damage to fear effect? Image, I have to fear enemies to gain the double damage but they are running everywhere. Do not want to play Tom and Jerry or hide and seek games. Once the resist from monsters, particularly RGs becomes immune to fear skills so how are we getting double damage to RGs?
Also can this set be set to all primary skills rather than frenzy only? We already have Blade of Warlord for bash, Dishonored Legacy for cleave, 300 spear for weapon throw and Oathkeep for all primary skills. Giving bonus to all primary skills would give a completely free choice for players to enjoy, even though there would be no other supportive items for those primary skills at the moment. However it leaves a open world with skeleton and add flesh and blood later days.
Perhaps, Undisputed Champion can be redeveloped to be all primary skills gain the effect of every rune?
Just my thoughts to barbarians.