No, it's mostly because of its revenge killing. With a LO he gets the power boost and is still blistering fast. So he can revenge without being locked into a move, making him that much harder to switch into until you know what coverage moves he's running.
Most Deoxys-S don't run Shadow Ball and your typical Aegislash is 3HKO'd by Fire Punch (assuming Kejmur's spread). On top of that, 252+ Atk Aegislash's Shadow Claw is a guaranteed OHKO (of course, in Blade Forme, but by then, it took two hits). Shadow Sneak does 73 - 87.1% against Kejmur's spread on Deoxys-S. For the rest of the calculations, when Deoxys-S attacks, it showcases the strongest possible attack on the typical Deoxys-S.
100 Atk Life Orb Deoxys-S Rock Slide vs. 252 HP / 0 Def Togekiss: 156-185 (41.7 - 49.4%) -- guaranteed 3HKO after Leftovers recovery
Togekiss switches in, tanks two Rock Slides to use Thunder Wave Deoxys-S, then Roosts until it hits enough health, and use Air Slash for Paraflinch. Just watch for Rock Slide Flinch.
176 SpA Life Orb Deoxys-S Psycho Boost vs. 252 HP / 252+ SpD Deoxys-D: 58-69 (19 - 22.6%) -- possible 6HKO after Leftovers recovery
Look at that! Deoxys-D can, so obviously, tank any hit from Deoxys-S and then use it as Hazard Fodder, using Recover to get some health back.
176 SpA Life Orb Deoxys-S Psycho Boost vs. 252 HP / 252+ SpD Jellicent: 156-185 (38.6 - 45.7%) -- guaranteed 3HKO after Leftovers recovery
Continuously use Recover until close to full, then finish it off with Shadow Ball.
100 Atk Life Orb Deoxys-S Fire Punch vs. 252 HP / 0 Def Metagross: 120-143 (32.9 - 39.2%) -- 12.3% chance to 3HKO after Leftovers recovery
Meteor Mash+Bullet Punch.
176 SpA Life Orb Deoxys-S Psycho Boost vs. 252 HP / 252+ SpD Mew: 81-95 (20 - 23.5%) -- possible 6HKO after Leftovers recovery
...I speak none of Mew's advantage.
176 SpA Life Orb Deoxys-S Psycho Boost vs. 252 HP / 0 SpD Reuniclus: 129-152 (30.4 - 35.8%) -- 35.9% chance to 3HKO
Recover, then attack.
100 Atk Life Orb Deoxys-S Fire Punch vs. 252 HP / 4 Def Sableye: 95-112 (31.2 - 36.8%) -- guaranteed 4HKO after Leftovers recovery
Foul Play it.
100 Atk Life Orb Deoxys-S Rock Slide vs. 0 HP / 0 Def Victini: 151-179 (44.2 - 52.4%) -- 18.4% chance to 2HKO
Revenge Switch.
100 Atk Life Orb Deoxys-S Fire Punch vs. 252 HP / 4 Def Wobbuffet: 116-136 (19.8 - 23.2%) -- possible 6HKO after Leftovers recovery
...be Wobbuffet.
176 SpA Life Orb Deoxys-S Psycho Boost vs. 4 HP / 252 SpD Eviolite Wynaut: 90-107 (27.1 - 32.2%) -- guaranteed 4HKO
Okay, that's just sad...
176 SpA Life Orb Deoxys-S Psycho Boost vs. 252 HP / 0 SpD Suicune: 199-235 (49.2 - 58.1%) -- 64.5% chance to 2HKO after Leftovers recovery
Revenge ResTalk for the win!
176 SpA Life Orb Deoxys-S Psycho Boost vs. 252 HP / 0 SpD Milotic: 187-220 (47.4 - 55.8%) -- 21.5% chance to 2HKO after Leftovers recovery
...here too!
100 Atk Life Orb Deoxys-S Superpower vs. 252 HP / 252+ Def Eviolite Chansey: 317-374 (45 - 53.1%) -- 30.5% chance to 2HKO
Superpower weakens, so you'll survive to Softboil.
Other Pokemon Deoxys-S has trouble 2HKOing includes Spiritomb and Steelix...not like it matters for them; they'll never touch OU.
Keep in mind the following moves were taken into consideration: Superpower, Psycho Boost, Thunderbolt, Ice Beam, Fire Punch, and Rock Slide. These Pokemon above are typically semi-safe switch-ins. Some might not be considered MetaMaterial, but this once again proves a statement made by Haunter:
Deoxys-S can be a terror for offensive teams but, unlike it's Attack and Normal counterparts, it lacks the firepower to break balanced/defensive teams, which is exactly why I said that, should Deoxys-S get banned, it certainly won't be because of its offensive presence. Again, its attacking stats are mediocre at best and unless it manages to hit its opponent for SE damage, it's not going to do much.
Deo-S was banned under the support characteristic in Gen V and supporting its team mates is still what it does best in this generation.
Most of the above Pokemon are being hit Super-Effectively (those that aren't are typically because Psycho Boost or are Bulky-Psychics). A few make for good Revenge-Switches while others can come in and threaten Deoxys-S...usually by stalling. What did you say before about "making him that much harder to switch into"? Well, these Pokemon can do it, but some of them will fail against the Support Sets. For example, Milotic, Chansey, Wobbuffet, Jellicent, and Deoxys-D would dislike their item being traded for Choice Scarf, anything missing Priority Taunt will hate getting Hazards, and the same group wouldn't like Screens up on them either. Even then, Magic Coat could stop that Taunt...Sableye.