Scarf Skymin's Seed Flare does not OHKO. Deoxys forms HAVE to run Scarf to outspeed and kill Doryuuzu. Darkrai HAS to run a Scarf and use a Focus Blast to kill Doryuuzu. Darkrai and Skymin don't even have a chance to attack unless Doryuuzu is running an Adamant nature . Any Inconsistent Pokemon that comes into Doryuuzu will die, and even with a +2 Speed boost won't be able to outspeed. Other than Deoxys-A, who gets setup upon by Ghosts; Deoxys-S, who's using a very gimmicky set JUST to kill Doryuuzu; and Deoxys-N, who's rather outclassed by S and A, nothing you just mentioned really threatens Doryuuzu.It is very fast and still powerful, but in this metagame with inconsistent, and other very large threats, it definantly hasn't had a chance to shine. But I do not believe it will be uber after the banning of inconsistent, shaymin-s, Darkrai, and deoxys. Far too much can check it.
Losing a steel type isn't a bonus lol. Sandslash couldn't fill Doryuuzu's place because of Doryuuzu's niche: The fastest Pokemon in the game.And even if it was banned, Sandslash can easily fill it's place, only losing to + speed base 105+ pokemon, and +2 pokemon (so it's not as good at revenge killing agility/rock polish pokes as dory). With an earth plate, it's earthquake rivals balloon dory's, and it's unboosted stone edge is stronger than doryuuzu's rockslide. It's coverage move is its only weaker move. However, it has increased bulk over the mole; no fighting and earth weaknesses really helps. As does not having to protect a balloon.