Leaper Barbarian

The Leaper Barbarian is really a high mobility build that jumps inside a pack of monsters inflicting massive harm to a single target, the AoE damage is extremely subpar in the present state. The developers could give a new War Cry synergy to enhance the AoE harm to help w/ swarming enemies. 

Leap Attack Synergies

Leap: +10% Damage per level

War Cry: +10% AoE Damage per level

Singer Barbarian

The Singer Barbarian is really a fun build, however, the damage ultimately tops out a little lower than you might like, which makes it less than optimal. To improve War Cry, the developers could replace Battle Cry synergy w/ Grim Ward because it doesn't take advantage of lowering enemy defense, however, it does take advantage of reducing enemy physical resistance. As War Cry damage is insanely low and also the fact monsters can block you, the brand new Grim Ward synergy would help to make monsters more susceptible by making the skill unblockable. Lastly, adjust the other two synergies as follows.

War Cry Synergies

Howl: +10% Damage per level

Taunt: +10% Damage per level

Grim Ward: -5% Enemy Block Chance per level

Concentrate Barbarian

If you’re a Concentrate Barbarian, you’re likely to want to use Iron Skin to increase your defense. Therefore, it seems sensible to replace the Bash synergy w/ Iron Skin because it better complements the skill while adjusting another synergy as shown below...

Concentrate Synergies

Battle Orders: +15% Damage per level

Berserk: +3% Magic Damage per level

Iron Skin: +1% PDR per level

Frenzy Barbarian

With the high attack and movement speed of the Frenzy Barbarian, this character can easily dispatch his foes. The main disadvantage to this skill may be the sheer number of skill points required to increase frenzy damage, often requiring you to definitely sacrifice Battle Orders. To improve Frenzy, the developers should remove Taunt synergy and adjust other synergies as follows. Players can buy d2r items and diablo 4 items from a trustworthy shop like MMOWTS to gain access to powerful new abilities and strategies.

Frenzy Synergies

Double Swing: +15% Damage per level

Berserk: +3% Magic Damage per level

Increased Stamina: +0.4 Seconds per level