No one's disputing the benefits of Dark Intent, it's just that the OP seems to think that DI is needed to make us competitive.
It is more directed towards the person saying that DI would not cause such a huge dps discrepancy between player A and B. True that other factors are important, but DI certainly can attribute to a huge dps boost.
And regarding competitive, it depends how people view it. If you mean in a sensible raid where sensible cooldowns (this means rogues tricksing each other and no PI), gear and buffs are available to boost their dps to the max potential as possible of their class, then yes, DI is kind of required to make them competitive with other players in the raid that strife for it. In other words: DI is highly sought (and in a sense required) to allow a player to maximize the potential of their class in sensible margin of what is available. It will be a matter of opinion of the designers what their sense of competitive is, and for every player it will be different as well. For one person it can be an element where it wont be needed to be competitive, for others it will be. in my eyes I deem it as needed to make us competitive as it allows me to maximize the potential of my class in reasonable margins.
Thats werid i never OOM as a shadow priest unless im just being an idiot with my spells
If you SW: Death on cooldown when you hit like... 30% mana, you can easily bring your manarz back up. Likewise, with the 2set bonus from the firelands set, and with some certain talents, your shadow fiend can basically come out to play for a good 50% of the battle.
I do think something needs to be done about mastery. I like your idea.
Also, they gave archangel to Disc because they want to make sure they follow their "NO PURE BUILDS EVER" model. So they stuck archangel in disc hap-hazardly to fit this, without really considering how to really make it benefit the actual disc tree.
To be honest, they may have considered making it function differently within disc itself, so its useful for both Disc and Shadow. As it is, you generally don't take advantage of smiting to build up archangel unless you're VERY confident you have the time and mana to do so. So basically, heroic dungeons.