Because aside from Warbreaker giving DW and Cleave no longer replacing Sweeping Strikes nothing has changed despite many, many, MANY reports of how the current state was deeply unsatisfying for PvE. This is based on every theory of activity execution and construction. While some people might like it subjectively, objectively playing Arms in PvE ticks off about every box in “this is a bad activity”. While in PvP all the things that make it problematic in PvE make it incredibly superior in PvP.
And it’s only going to get worse from here on. And this is mathable. I’ll use the interaction between OP and MS for this example.
If MS right now deals 4k damage, with nothing else applied, then a +40% damage increase is a 1.6k point increase.
In two patches time, MS deals 7k damage. Then exact same +40% increase is now a 2800 point increase.
Nothing itself has changed about the buff. The buff itself is the same +40% it was before. The only thing that has changed is the base value according to the principles of Skinner’s Box.
It’s relatively easy to set up a situation where multiple of these exponential modifiers are stacked, at least Blizzard changed them from being multiplicative to addictive, in PvE this would be a loss of DPS as you’d have to break your rotation to do so. In PvP your rotation can easily be outhealed, unless you use cooldowns, so you can toss DPS out the window as what matters is the beefy hits, at least for use since we attack slow in the first place. So you want to make the next hit as impactful as possible, at least if you’re going for the kill.
Other classes can only do this by aligning abilities that all have a long CD. Arms can do this consistently instead. The longest cd is Avatar and having to sit that one out is no great loss.
If I have to give a value to what’s being done objectively in the design of Arms I would say it was nuts. Exponential modifiers already have no place in an MMO, and the ARms spec is heavily built on them.