The problem is PARTLY AR. Adrenaline Rush, at its core, is meant to double your playstyle. This means that in general, you should have half your globals open. You can mitigate this by dropping to low energy values BEFORE pressing AR- back in the old days before we had to build shit around AQ color scarabs, you'd want to be at like 10-20 energy with 1-2 combo points when you would press AR.
The glyph where the GCD becomes 0.7 Seconds is an attempt to address this- it recognizes that in modern WoW, energy can't just be fucking DOUBLED without a problem, and as such it creates a bigger space to play in.
I think, overall, that this is fine. I like Adrenaline Rush. I think it should give you a bigger energy cap for a little bit, or automatically trigger a 20 energy suboptimal move off global, or there should be a move you can press off the global during it. I don't want to give up the double part, and I really like the way it looks with blades.
But with the T15 thing, you have a half second GCD, which should make a big difference (and sometimes does), but the core problem is that you are making 2 combo points (sometimes three) with every sinister, and the sinisters cost like 24 energy, and your energy regen has been doubled to more than that. That's three things: doubled regen, moves cost around half, moves make more combo points (meaning that eviscerate, which is energy positive, happens every 2-3 globals instead of every 8 or something). That stack is why it's dumb, and the below things are cooler than nerfing AR:
1)- Capping energy deals burst damage to the target. The burst damage wouldn't be super efficient, and would knock off around 20 energy.
2)- Energy bar length grows at 10 / second during AR, and shrinks at 10 / second when it ends. Or just combat has a bigger energy bar.
3)- A move can be used off global, such as revealing strike. This would likely solve the issue best.
4)- We have access to a different move that costs a lot of energy, does more damage, but is generally not that efficient.