There has been some talk on PO lately about Deoxys-D being worthy of a suspect test for the same reasons it was banned in the previous generations: its ability to lay down entry hazards very easily, giving HO teams the edge against the other playstyles.
When almost everyone had their eyes on Deoxys-S at the start of XY, more savvy players caught on the fact that Deo-D was actually the better one of the two.
While Deoxys-S is more versatile as it can run either an offensive set or the same hazard support set Deo-D runs, the former has issues with the often disappointingly low damage and reliance on a really bad STAB move against anything not weak to its coverage options and the latter can be shut down by any decent offensive pokemon with access to priority, often limiting it to just SR or one layer of Spikes.
Deoxys-D has no such issues. Thanks to its bulk it isn't forced to run Focus Sash and it still has enough speed to outpace most Taunt users. Even against faster Taunters and Pranksters it can still come out on top with Magic Coat. It is true that Deoxys-S can run Taunt or Magic Coat too, but its low bulk means that a misprediction (for example, against Thundurus-I) could turn into disaster, while Deo-D can usually get away with one.
Deo-D also doesn't mind Foul Play thanks to its crap attack stat and high bulk, so it can afford to stay in against something like Mandibuzz, Taunt her and proceed to lay down hazards, something Deo-S can't do.
Deo-D can also run the annoying combination of Taunt+Recover+Rocky Helmet, which turns Excadrill, the best spinner in OU, into a total joke.
And there's still the dreaded Red Card set that can royally screw up set-up sweepers, who will try to attack Deo-D as quickly as possible (lest give it more turns to lay down more hazards), probably fail to even 2HKO and be phazed out.
Basically Deo-D always runs SR and Spikes, and the last two moveslots plus its item slot can be customized in order to completely crap all over the playstyle your team has most issues with.
But no matter what, Deoxys-D will never be deadweight, it will always lay down hazards unless played in spectacularly poor fashion, and its buddies Bisharp and Thundurus will punish anything that tries to Defog them.
Been said that, I personally consider Deoxys-D worthy of a suspect test, but not necessarily broken. It would be interesting being able to play a suspect test where people are forced to run Deoxys-S over Deo-D and see how it plays out.