Many of the better Steels have plenty of SpD. Metagross, Magnezone, Jirachi, Empoleon, and Heatran all have very respectable SpD. Bronzong is a wall on both fronts. What's left, Skarmory?
All of those still takes a lot of damage.
Metagross with 252 sp. def EVs lose 142 - 167 Hp from a Choice Specs Draco Meteor.
@topic:
In D/P it's extremely hard to get a turn for Manaphy use Tail Glow. If someone from the opposite team already has used a Nasty Plot/Swords Dance, Manaphy can't do a thing but get 2HKOEd. And before using Tail Glow, he won't KO anything with his mediocre 100 base sp. atk (while Azelf gets 125, which is enough to KO something that already endured any attack even unboosted).
We can compare Manaphy to Swift Swim Pokemon. Bulky, packs a powerful Surf/Hydro Pump that can be used right from the bat, and is enough to 2HKO even those resistant to it, also they aren't outrun by nothing. While Manaphy has a mediocre 100 sp. atk (while Azelf has 125, enough to KO opponents even unboosted), he needs to Tail Glow every time he'll want to attack, his speed will let him open to powerful hits like Choice Banded Garchomp's Outrage, Alakazam's any attack or Gengar's. Even Azelf with Thunderbolt will take out a lot of Hp from him (OHKO if Nasty Plotted once).
So, if Manaphy pops up in a Rain Dance team, he'll probably be the Resting one. And then he'll suffer from the four move slot sindrome, which has been explained some pages ago.
Sorry for the long post.