We still see a lot of people asking about if they should have three magicka Necromancers wearing Master Architect or when a healer should use Roaring Opportunist and Jorvuld's together versus Roaring Opportunist and Z'en's Redress and a general curiosity of how endgame raid teams use these sets and will use these sets going forward with the nerf to Major Slayer in Update 28 or Markarth DLC next patch.
So to start off, let's look at Roaring Opportunist, this set was changed for the better right before Update 27 or Stonethorn DLC with its duration per proc scaling off of spell damage or max magicka rather than how much damage you do with your heavy attacks.
With Roaring Opportunist it's true that you can proc it a second time for a second set of DPS with a 2nd heavy attack after the first heavy attack and not have it affect the first set of people, how it decides that isn't really "smart it's simply just affecting people who don't have Major Slayer if that makes sense.
The next sets we need to look at are Master Architect or it's stamina DPS equivalent War Machine.
Now, ideally if you want the most damage out of using these sets, you want to pre-buff Master Architect on two people, typically two supports or one support plus a Necromancer.
And if you don't know what a pre-buff set is, definitely check out Nefas's post on pre-buff sets.
Basically you need to have an addon like Dressing Room or AlphaGear and you need to use your pre-buff ultimate (whether it's a Colossus, Warhorn or whatever) which should typically be at 500 Ultimate meaning you get about 50 seconds of Major Slayer after cast, (this requires you to make sure to have close to 500 Ultimate before the boss fight) right before the boss spawns in or exactly 2 seconds before the group engages the fight letting you swap back to your actual build for the fight.
If the group can't kill the boss in less than 50 seconds or the fight is going to be longer than 50 seconds like Rakkhat Hard Mode or Z'Maja in Cloudrest, we definitely recommend a healer in Roaring Opportunist and Jorvuld's after the initial pre-buff.
After some extensive testing this patch in raids we've concluded that RO/Z'en's or RO + a damage set is situational and will be dependent on the fights/Trials including who would wear it (the offtank support or healer).
In the following video, you will see Nefas do his usual prebuffs but sometime later he heavy attacks twice to proc Roaring Opportunist to align with the next Major Vulnerability because the initial Major Slayer from the Master Architect prebuff has gone away at this point.
It's quite an understatement for us to say that the above requires a lot of organization within your group plus you need to be on PC to do pre-buffs and unfortunately console players do not have access to addons to enable them in doing this.
And of course for places like vAS Hard Mode, it's probably better off using Master Architect or War Machine during the fight for most groups. In general for most groups anyway, it's definitely less of a headache to simply have three people in MA and War Machine.
Furthermore, for next patch, otherwise known as Markarth DLC, we see a lot of people saying that they think Major Slayer won't be worth it because it's 15% is getting nerfed to 10% but we still think we will prebuff War Machines and Master Architects depending on whether you're a stamina or magicka DPS composition and we'll probably still see the use of Roaring Opportunist probably as you still ideally want all buffs and debuffs possible when scorepushing or trying to get the most out of your damage.