The four-piece isn't worth it because even a 150% damage Divine Storm won't do as much damage as a regular Templar's Verdict.
This is simply a fallacious argument. Since the proc is free and not dependent on holy power, the only cost it has is a global cooldown. Therefore, the empowered Divine Storm doesn't have to do as much damage as Templar's Verdict in order for the set bonus to be a DPS increase, and finding where it may fall in our priority could tell us just how valuable this proc may be.
Luckily the fine folks at EJ have already done some preliminary testing using PTR data and have found that it is not at the bottom of our action list. In fact, early sims show that it could snuggle comfortably between Hammer of Wrath and Crusader Strike (since the lower portion of our priority has been shaken up thanks to iterative buffing of Sword of Light).
Of course, the devs have yet to make their tuning pass on the PTR so these numbers could change, but I would be very surprised if they actually did.
The only use for this bonus will be on cleave fights and trash pulls, and won't matter on the "important" encounters.
As shown above, even on single-target encounters the bonus does pretty well with estimates ranging from a 3.5% to a 5% DPS increase (a fairly typical range for four-piece bonuses), Divine Purpose synergizing very well with the bonus and giving us the latter result. Naturally, on fights with two or more targets this damage boost will strengthen and increase the DPS contribution of our four-piece considerably.
If this tier bonus was introduced at the start of Throne of Thunder, I have no doubt that the same concerns about cleave would have cropped up. However, looking back now we can see that 6 out of 12 normal mode fights benefitted from cleave damage. From what I've seen watching Blood Legion's raid test videos from Siege of Orgrimmar, that number jumps to 9 out of 14 in the next tier. Somewhere in those nine fights must be an "important" encounter, right?
Being forced to use an AoE attack in a single-target rotation is "clunky."
This is the only argument that has some traction, even though I still disagree with it in this case. During Cataclysm, when retribution still had access to Holy Wrath and Consecration this argument eventually got the abilities removed from our toolkit altogether, which thus far has been both a relief and a source of frustration. Increased holy power generation and expenditure, coupled with our newfound love of haste, steadily sealed the gaps left by these two abilities, but their absence is definitely felt in niche situations where holy power is at a premium and you have no targets with which to smack with Hammer of the Righteous.
In Mists and beyond, we are looking at two distinct styles of play in most PvE situations – single-target and AoE. Depending on your number of targets, you either use Crusader Strike or Hammer of the Righteous, Templar's Verdict or Divine Storm, and Seal of Truth or Seal of Righteousness. There are no ifs, ands, or buts about it – we drew our own line in the sand, forcing our playstyle to adhere to one side or the other.
While some of this is only natural (you either have one target or you have many), it makes things a bit dull. The whole point of set bonuses is to throw a wrench in the works, to rustle the jimmies of our conventional thinking and for us to find a way to use this new mechanic to our advantage. In the past, flat damage boosts have been criticized as simplistic and boring, so Blizzard has put in an effort to make set bonuses more interesting and engaging. This tier, instead of changing the way one of our main rotational abilities works, is introducing a variation that we haven't seen for a long time – using an ability outside of its predefined operational range.
Indulge me for a moment while I wax philosophically, but are we as a community so concerned about numbers and ranks that we're afraid of change and challenge? Have we spent so much time mapping and plotting the interior of our box that we're afraid to peer over the precipice and dip our toes into the unknown?
While it's nice to have a steady, reliable rotational framework that flows well, repetition can lead to boredom and burnout. Instead of trying to continually alter the spec's baseline to keep veteran players interested, set bonuses provide the devs a means to temporarily kick things up a notch. Variety is the spice of life after all, is it not?
The Light and How to Swing It teaches you the ins and outs of retribution paladins, from Ret 101 and how to gem, enchant and reforge your retadin, to essential ret pally addons.