Just a ONE off post by me.
I feel i should elaborate on why its suspect a bit more, basically the standards Deoxys-D sets are the following.
Set 1.
Max hp / Max speed @ Mental Herb or Rocky Helmet
~ Spikes
~ Taunt
~ Stealth Rock
~ Magic Coat / Night Shade
Set 2.
Max special attack / max speed @ Life Orb
~ Spikes
~ Stealth Rock
~ Hidden Power Fire / Thunder
~ Psycho Boost
Set 3.
Max hp and speed @ Light CLay
~ Reflect
~ Light Screen
~ Taunt
~ Stealth Rock
Set 4.
Max hp and sp.def @ Lefties
~ Spikes
~ Taunt
~ Recover
~ Night Shade
So lets get a few things out of the way.
Taunt is irrelevant against Deoxys-D. You CANNOT Taunt it if you are playing someone competant. All standard sets are faster than every single Taunt user in OU (bar Prankster users but who uses those in OU bar like Sableye and better yet which are even viable ? Dont try and tell me stuff like Leipard is viable in OU....please). Even if you find something retarded enough to BE faster and Taunt Deoxys-D, it either will use Magic Coat to REFLECT your own Taunt back at you, has Mental Herb so it can escape the effects of Taunt or just simply hit you with a Life Orb Psycho Boost. Deoxys-D is essentially guaranteed two layers of hazards if you dont have....basically....CBTar or MB Espeon? Scizor doesnt OHKO so yeahhh.
Which brings me to my next point. How terrible Rapid Spin is and Life Orb Deoxys-D power. If you switch ANY rapid spinner in against this thing Life Orb Psycho Boost/Thunder is a OHKO. Hidden Power Fire is also sometimes present to nail Ferro, Scizor and Forry. If you try and Taunt this set you are gonna get wasted by brute force. For those of you all like "but D-D has bad offenses". No try saying that to a 140 BP (stronger than Draco Meteor) STAB Life Orb boosted move. To put this in perspective, LO Psycho Boost from modest D-D strips around 80% from standard Garchomp who is considered a VERY bulky sweeper. ._. On that same note of Rapid Spin being bad. There really arent many viable users of the move and as i said every spinner in OU is hit SE by LO D-D. Not only that but if your opponent is competent he/she WILL use a ghost to block rapid spin on the same team, its really that simple. Also really try keeping your spinner alive in a game where you are constantly taking Rugged Helmet damage from D-D if they dont have an anti spin. Its really one of the most uphill battles you will ever try and do lol...
Lastly, its unpredictable. Imagine you both lead, knowing your opponent will lead with D-D and you with your CBTar. Now you think to yourself "oh ill just Crunch/PUrsuit for an easy kill whilst he sets up just SR or spikes." Then you get hit with a Reflect. Crunch under Reflect does 75% max to max hp/0def Deoxys-D. Yeah...he will get Dual Screens on your ass and maybe a Terrakion behind those screens with an SD or a Sub or maybe a Garchomp or Cloyster, sounds fun doesnt it ? Scizor fares even worse. On the flip side you could be expecting a dual screener and go to your cute little prankster user/Spinner and get hit with LO Psycho Boost or just be owned by Magic Coat or Mental Herb Taunt whilst he stacks hazards on you.
All the above points combined are why its suspects.
TL;DR if you are using a cosmic power staller set you are doing it wrong. D-D is ALL about hazards and team support and which is why its suspect.
Personally wouldnt mind if it goes. Its a pain to beat even when you know the set. However i do like it as the Defensive Taunt set shuts down CM Reuniclus and other things.