I think people don't realize its power yet. Some pokemon may be too sucky for Ubers, but that doesn't mean they should be OU (Mew for example). Being the fastest in the game, mainly in the OU metagame, potentially puts a stop to all the DD / Scarf users, namely Gyarados and Garchomp. I don't know about you, but if someone, somehow, managed to get 2 DD's on Gyara and then suddently Deoxys comes out of nowhere forcing a switch, I'd be quite pissed if I was the Gyara user. This pokemon take a lot from the OU metagame instead of contributing to it IMO.
Also, Deoxys-E stats aren't SO bad. 90 in both defences and 50 HP can be compared to Starmie, and Starmie usually keeps it HP unmaxed at 304 (which is ironically the max HP of Deoxys-E). A defensive set with enough power to KO Gyarados/Garchomp can be quite terrorizing, as Deoxys-E even learns Spikes, something every team should fear. Thunderbolt is not only threatening Gyara, but also Skarmory who usually tries to set up her own spikes or whirlwind you away.
There are better mixed sweepers in the OU metagame, but they don't have access to moves like Spikes and Knock, nor do they have the ability to pressure stall.
Now, for the team.
Deoxys-E: Superpower is highly overrated IMO. Blissey switching in on Superpower has a very slim chance of happening. If it's 1v1 then Blissey can simply use Softboiled and laugh at Deoxys why it is left with -1 Atk and Def. I agree that it needs a way of handling Weavile/TTar, so why not give it Focus Blast? Gengar doesn't complain about the 70% accuracy, why should Deoxys-E be any different? Blissey will fear it a lot more with some calm minds passed to it.
Gliscor: It doesn't need jolly, go impish. The only thing it should outspeed is jolly TTar so it can Roost off damage from Stone Edge. Also, it doesn't need Aerial Ace to counter Heracross. At long as Hera is faster, he will not be doing much damage, and your Earthquakes will kill him eventually. You can switch it for Stealth Rock or Ice Fang, but keeping it isn't a bad idea.
Celebi: It should have a way of healing itself, so Recover > HP ice IMO. You already have Ice Shard on Weavile and Ice Beam on Deoxys-E.
Weavile: I personally think Pursuit is a must on any Weavile, but your set can work I guess. Just be careful because you won't get many opportunities to use Swords Dance being left unharmed.