SSJ I like how you say that M-Aggron would beat Doublade, when it is actually the opposite in most cases.
Turn 1, Doublade SDs as you switch to M-Aggron
Turn 2, M-Aggron Earthquakes and Doublade SDs again
Turn 3 + 4, M-Aggron fails to 3HKO and Doublade cleanly 2HKOes with Sacred Sword
+4 252+ Atk Doublade Sacred Sword vs. 252 HP / 136+ Def Filter Mega Aggron: 175-207 (50.8 - 60.1%) -- guaranteed 2HKO
0 Atk Mega Aggron Earthquake vs. 240 HP / 0 Def Eviolite Doublade: 90-108 (28.2 - 33.8%) -- 0.3% chance to 3HKO
And eww, Gyro Ball Doublade. Iron Head is the way to go, which hits notable fairies harder too. As Chesnaught does pitiful amounts with Wood Hammer and relies on Leech Seed to kill over a few turns, Doublade easily gets to +4 and 2HKOes yet again:
+4 252+ Atk Doublade Iron Head vs. 252 HP / 252+ Def Chesnaught: 240-283 (63.1 - 74.4%) -- guaranteed 2HKO after Leftovers recovery
If you have phazing on either Pokemon Doublade is easily wish healed back by clerics which pair very well with it, and can dent the physical walls after a +2 and an Iron Head/Sacred Sword to boot as it is phazed.
Now I'm not saying that Doublade is with its flaws, and bulky waters, and Dark-types and burns are 3 of its greatest draw backs, admittedly, though I do not think that this is enough to make it unviable as people seem to make it out to be.
Special Attackers in general aren't that big of a thorn in Doublade's backside either. Granted Doublade won't be switching in on many and setting up, but using the example of your Kingdra, granted I got the +2 on the physical mon I just forced out, I survive your Surf and then:
+2 252+ Atk Doublade Sacred Sword vs. 64 HP / 0 Def Kingdra: 200-236 (65.1 - 76.8%) -- guaranteed 2HKO followed by
+2 252+ Atk Doublade Shadow Sneak vs. 64 HP / 0 Def Kingdra: 135-159 (43.9 - 51.7%) -- 9% chance to 2HKO
= bye bye Kingdra
Granted I am not saying it is a flawless S-Rank Pokemon, as it does have flaws, but it has a rather valuable and reliable niche in the metagame that should warrant it at least B rank, where it would be at home with other mons with successful niches such as Toxicroak, Shuckle and Diancie (god knows why Diancie is even higher than Doublade atm) who have a similar amount of flaws (though imo they have more).
No, I will not stop until my two swords of justice are moved up