So, just to clarify, do the people that find Deoxys-S broken, find its Lead, Attacker, or the combo of both broken? Because each single set is not broken on its own.
Laurel said that offensive Deo-S is impossible to switch into, which simply isn't true. Aegislash, Slowbro, Mega Mawile, BU Talonflame, SpD Skarmory, Goodra, AV Tangrowth, AV Azumarill, Jirachi, and SpD Celebi are just some of its solid checks/counters. And even if you can't fit one of those for some reason, no worries. Deo-S is very easy to revenge kill with Talonflame, CB Dragonite, CB Azumarill, Bisharp, and other strong priority users, as its mediocre bulk, lack of resistances, and vulnerability to all kinds of passive damage make it very easy to wear down and pick off with priority. Not to mention that two of its moves, inlcuding its only STAB move, have severe drawbacks, which make it very prediction reliant and very easy to revenge kill or force out. If it kills something with Superpower it dies horribly to priority. If it kills something with Psycho Boost, it is forced out. And that's in the best case scenarion, assuming the Deo-S player predicts correctly and doesn't drop its Atk / SpA before it KOes the Pokemon it needs them for. And it's not like Deo-S gets many switch-in chances, due to its mediocre bulk and lack of resistances, so it usually only gets 1-2 switch in chances to do its job.
So, between its plethora of checks and counters, vulnerability to priority, lack of switch-in chances, and reliance on moves with drawbacks, Deo-S is not broken at all as an all out attacker. It's just a great revenge killer and a good cleaner, that definitely needs a lot of support in order to clean up.
As for the lead set, i really don't get how someone can find it broken. Most of the time it's job is to set up SR while preventing you from setting up SR. So, guaranteed SR is now broken? There are many other good leads that can consistenly set up SR, prevent the opponent from doing so, and even fare better against Rapid Spiners. Sash Aerodactyl gets outsped only by Deo-S, has both Taunt + SR, and can even beat the most common spinner, Excadrill with either Earthquake or Fire Blast (depending on if it has Air Balloon or not), while not getting fucked up by Tyranitar, which limits Deo-S to only SR (while it can set up SR after Deo-S dies, thanks to its own Sash). Taunt + SR Terrakion is in a similar boat, being an excellent SR setter than can prevent every single spinner / Defog user from getting rid of SR, which can actually check dangerous offensive threats (Mega Char Y, Genesect, Volcarona, and Heatran), unlike Deo-S. Yeah, Deo-S doesn't always have to lead, but if the opponent sets up SR before Deo-S comes in, then your Sash is useless and you can get OHKOed by plenty of offensive Pokemon. And it's not like Pokemon such as Lati@s and Excadrill can't find time to get rid of SR against offensive teams, as both check a multitude of offensive Pokemon. Yeah, Lati@s can possibly give to Bisharp a +2 boost, but Latias can as easily use Healing Wish after it gets rid of SR to bring in a faster Pokemon than Bisharp which resists Sucker Punch, such as Greninja, Choice Scarf Tyranitar, Terrakion, Keldeo, or Infernape. Or the Lati@s user could just pack a Bisharp counter. Or predict the Bisharp switch and use Hidden Power Fire. So all in all, the battle of getting rid of SR is really not that hard, not to mention that even if you don't manage to get rid of SR, it's not that big of a deal, and as i already said, other Pokemon can already do this.
Finally, i don't believe that the versatility granted by having two great and very different sets makes Deo-S broken. The lead set is fairly easy to spot, as it usually leads, and its team often lacks another SR user, which makes it incredibly obvious it's the lead set. And even if the opponent somehow manages to surprise you with their Deo-S, it's not like you will pay a big price. If you confused a lead set for an attacking set, then the opponent will simply set up one more layer of hazards, which is not hard at all to get rid of later, and if you confused the attacking set for a lead set, at worse you will lose a Pokemon, assuming you didn't first scout Deo-S's set with your check/counter, which is always an option. So, no matter what, you have the option of finding out Deo-S set with minor losses.
For those reasons, my opinion is that
Deoxys-S is not broken.
Oh, and
Jukain, the GtG vs idiotfrommars game is really not a good example to showcase Deo-S's brokeness, as the team who lost had no way at all to deal with hazards and no solid answer to Mega Lucario.