The Rule of Cool isn’t about balancing damage numbers. It’s about allowing cool stuff to happen even if it breaks the rules or seems problematic. “I one-shot everything” or “I am immune to all damage” aren’t cool, they are just broken. Allowing players to find broken combinations of character powers is cool, but the whole point of a seasonal game is to try to balance out those combinations the following season.
So, for example, S4 introduced tempers and specifically it introduce very powerful weapon tempers. Barbs, due to their cool mechanic of having a bunch of weapons, get to make use of many more weapon tempers, making they far more powerful than the other classes. Druid, Sorc, and Necro get 4 weapon tempers total. Rogue gets 8. Barb gets 12 (or really 4 1x tempers and 4 2x tempers). It’s a massive increase in both power and in the flexibility of how you make your build, allowing you to wield a unique and also get some 2x chance to cast tempers and also get some bonus damage tempers and so on. Other classes have to choose one of these things. If you wield a 2H unique, you get zero weapon tempers.
They are also beefing up every unique to compete with legendaries and adding a bunch of new uniques and aspects that can help support new builds. Overall, this is going to further increase the power of Barbs relative to everyone else because it is making weapons even more powerful.
So, how to balance that?
One option: massively nerf all Barb weapon tempers so that in order to get the same value as the other classes they would need to commit all their tempers to it. This runs into two problems: (1) there are tempers available to all classes that the Barb could still use, and (2) it massively constrains Barb builds, making it harder to make use of tempers across their weapons. This would have a small impact on damage and a larger impact on the coolness of having the extra weapons.
Second option: only allow the affixes from the weapon used by a skill to count. This would be more fair and still give Barbs some flexibility, but it would also dramatically reduce the value of the extra weapons, since most builds do most of their damage with one of the arsenal options. This reduces Barb damage but also reduces the coolness of their class mechanic.
Third option: nerf every Barb skill to subtract out the value of 2 2H-worth of tempers. This is possible, but extremely complicated due to the number of different combinations of skill and temper choices. They could focus on the meta builds, though, and just assume that non-meta builds are fine as they are. This is potentially a way to fix damage without removing anything cool, though it feels particularly bad for the skills nerfed and it likely results in some skills that were previously unchosen because there were more broken options to still remain broken (just slightly less-so).
Fourth option: Enhance every other class to compensate for the lost aspects and tempers. Tempers are about as powerful as aspects, which give about a 25% damage boost each as a baseline, doubled on 2Hers. 1.5 * 1.5 * 1.5 * 1.5 ~= 5x damage relative to Druids, Sorcs, and Necros, so they could multiply all skill values by 5 for those classes. This means that everyone can now one-shot the tormented bosses and we go back to having an endgame content issue. It also isn’t cool because it’s just more damage, and it constrains future solutions like new or beefed up mechanics for the other classes because they are already doing godly damage, so those mechanics would feel worse due to coming with major nerfs.
Fifth option: Introduce major new / enhanced mechanics for the classes that are less powerful than Barb, and tune them so that they are equally powerful to Barb now. This is certainly much, much cooler than nerfs, but it runs into the same issue as the blanket damage boosts: Barbs are just too strong in S4 for that to be the baseline.
Sixth option: Focus all the unique buffs and new uniques / aspects only on the under-performing classes, to bring them up closer to Barb’s level. This is cool for those classes, but it means that Barbs get zero new toys, and if it results in Barbs still being super powerful it has the same issues with invalidating endgame content. Options 5 and 6 satisfy the coolness factor but fail on the reigning in power factor.
Seventh option, the one they seem to be going with: Buff the other classes a little (main stat scaling, skill buffs), nerf Barb key passives so that the number of things nerfed is smaller and more controllable but still provides a blanket reduction to the class’s damage and minimizes the impact on different builds relative to each other. This isn’t cool in itself, because it’s just blanket damage buffs and nerfs, but it does a much better job of preserving the coolness of existing stuff like Barb weapons while bringing down the top-end baseline to a point where the pinnacle bosses will still be very challenging to all classes.
Going with option 7 allows them to address the balance a bit for Season 5 without tying their hands for Season 6, when the expansion will change everything anyway. It leaves room for the future mechanics enhancements they talked about (in Season 6 or 7) without dramatically pushing the power level of everything yet again.
Overall, what is more cool: Keep all current power, introduce nothing new or Reduce current power, but add new stuff? Barbs can now play with Crown of Lucion, Locran’s Talisman, Shard of Verathiel, The Third Blade, and all the beefed up uniques from the existing game. They lost some power relative to S4 builds with S4 items (and GW lost a ton of power), but overall it isn’t clear what the power level will be until we get to play with the new toys. That’s a much more interesting / cool place to be. There are challenges out there to overcome, new builds to discover.