“Deoxys-D is an unviable Pokémon in Ubers due to having to many flaws that seriously harm it’s only valuable niche as a bulky spikes setter”-Smogon
“Deoxys-D’s seemingly excellent bulk, having base 160 Special Defense and Defense, is hindered greatly by its low base 50 HP”-Smogon
Deoxys-D isn’t very fast, and investing in speed would take away from investing in more defenses. It can be outsped and defeated before it can do much.
“Deoxys-S is a brilliant dedicated lead due to the fact that it has the highest base Speed in the game and access to utility moves such as Stealth Rock, Spikes, Taunt, Skill Swap, Magic Coat, and dual screens.”
Deoxys S has that amazing speed that allows it to outspeed almost everything and set screens, rocks, and spikes, etc. Even though it has mediocre defenses, it can hold a sash and is garunteed to set atleast 2 things up. It’s ability to oustpeed and set screens is helpful for its defensive capabilities.