Icy Man, I just wanted to say thank you for providing such a great debate for me. This will probalby be one of my last posts in this thread, but who knows.
Indeed you are right, I have run nearly out of arguments for Deoxys-D not being uber. However I have one more argument (admittedly, it is last resort, and I am kind of ashamed of that, but it is probably the most important argument against Deoxys) Here it is, from Jumpman's post.
Support Characteristic
A Pokémon is uber if, in common battle conditions, it can consistently set up a situation in which it makes it substantially easier for other pokemon to sweep.
Note that it meets this characteristic in a different way then other support pokemon.
In my opinion Deoxys makes it substantially easier for other pokemon to sweep, that is why I made a fake team. I purposely set it up so that this team could counter what was thrown at Deoxys-D and hit back MUCH harder.
In other words, you've used team synergy to turn Deoxys-L's weaknesses into advantages. Nothing new here.
As you can see with the team, it is appropriately designed to counter Toxic Spikes. Once those are out of the way, just Normals and Choicers bar Deoxy's way.
Normals, as we have discussed, have their problems. Taunt disables them all to a certain degree and makes the incoming pokemon much easier to stop.
Normals are an issue in the event that Night Shade is used as the offensive attack; ghost become a problem is Seismic Toss is the only one.
Choice Users are easy to counter because they are choice users, I think we have gone over that.
But they are still just as effective at hitting Deoxys-L crazy hard, and giving a choiced user a chance at a boosted hit (usually backed by STAB) is never a good thing.
For my problem with Deoxys, I want to pay attention to the facts that in order to be uber it has to consistently set up, for other pokemon, to sweep. (those are seperated by commas as to prove the seperate elements.
Taunt, first of all, is what allows it to set up. It sets the cycle of Force Me Out, or Die. That is set up.
With the above paragraphs, and previous posts, I think we can all agree that it can consistently allow set up, for other pokemon like Zapdos, Heracross, Haryiama, It also can occasionally setup for itself.
Finally, can the pokemon it sets up for sweep. Yes. That is why I specifically picked SD Heracross, a pokemon that might have had a harder time switching in to take advantage of it. Of course, almost any setuper could work well.
SD Heracross, though, isn't the best choice; it isn't Deoxys-L's setup that aided Hera so much, it is the fact that it takes advantage of the other team's TSpikes. Again, team synergy is the cause of this.
You also say (forgive me for not putting this in quotes, I'm saving space) Toxicroak can become Uber when properly supported with Dual Screens, a passed speed boost, and rain support, but Toxicroak isn't Uber itself - the support just allowed it to sweep.
However, I would like to compare the situation to a pokemon, we banned Uber before. It is often considered a mistake, but there is one specific issue that allows it to become uber, supplied by another pokemon. The Uber I am talking about is Garchomp, with Sand Veil. In my personal opinion, Sand Veil is alot of the reason Garchomp is uber. Too many good things attatached to one pokemon made it too much for the metagame to handle. Furthermore, Sand Stream was EASY to set up. On the other hand, setting up Dual Screen, a Speed Boost, and Rain Dance at the same time; that would be difficult! Deoxys E on the other hand provides easy setup, as I have shown you. In truth, it is how easily it can manipulate these other pokemon that makes it uber.
This was not the main reason why Garchomp was banned; its ability to effortlessly sweep a large portion of the metagame (practically all of it) using the Yache set is what classifies it as Uber under our current definition.
Also, Taunt clearly is the differer between this and other wall/stall/supporters. Sure, others learn Taunt, but none are used in this drastic unusual way, not even Cressalia. Therefore, it makes no difference that Deoxys is low in the Defensive tiers; it is able to work better, which matters more.
A valid point, although if it isn't already in, it won't be Taunting any sweepers due to its low speed. In order to wall and stall out a significant portion of the metagame, it must be able to switch in and take hits. It does this averagely at best.
Overall, I think in certain ways it is uber, in others, not; I can see things running both ways, and could see Deoxys-E decentralizing certain threats, while centralizing others. Ultimately, I think it is a very useful and underestimated pokemon, even in ubers, simply because how easily it sets up.
Whether this is my last post here or not (but I think it won't be), I have enjoyed discussing this topic with you. Thanks for that.
EDIT for Crafty Veteran: Unfortuanately, Deoxys still cannot gain enought power to bcome an offensive threat. Also in mention is the offensive threats me and Icy Man have been discussing. We are discussin a different Deoxy's set, but similar counters apply. And Pursuit CB T-tar will always be the bain of Deoxys-D. And also, a versatile wall, is in my opinion, is what OU DEFINATELY needs, for all the powerful mixed attackers. Oh, also, If T-tar switched in, it still wouldn't get huge damage from a +1 HP Fighting. It's pursuit will also do upwards 75% without taking Sandstream into account. Ultimately, if the metagame had been less offensive, maybe, but today, it probably would not work :(