Most of that is plain wrong tbh. The most common way specs Ogre beats Palkia is by overpowering it, i.e. hitting it with a Thunder on the switch and later on take it out with a Water Spout or Surf.
Not even that, tbh:
252+ SpA Choice Specs Kyogre Water Spout (150 BP) vs. 0 HP / 0 SpD Palkia in Rain: 143-169 (44.5 - 52.6%) -- 21.5% chance to 2HKO
...whereas:
252+ SpA Choice Specs Kyogre Water Spout (150 BP) vs. 0 HP / 0 SpD Assault Vest Palkia in Rain: 95-112 (29.5 - 34.8%) -- 15.3% chance to 3HKO
The difference in tanking ability is huge. However, I do think the item choice comes down to personal preference since Palkia can run many different items effectively. I personally think Assault Vest is much better on teams that have multiple Water weaknesses or just have Palkia as the sole Kyogre switch-in, where AV is really needed so Palkia doesn't get murdered too quickly. If you have backup Kyogre checks or really need the extra damage on certain things, Lustrous Orb would be better then.
That being said, these calcs on AV Palkia are quite interesting, showing just how much special bulk Palkia has with it:
+2 252 SpA Life Orb Darkrai Dark Pulse vs. 0 HP / 0 SpD Assault Vest Palkia: 199-235 (61.9 - 73.2%) -- guaranteed 2HKO
4 SpA Stone Plate Arceus-Rock Judgment vs. 0 HP / 0 SpD Assault Vest Palkia: 87-103 (27.1 - 32%)
252 SpA Dialga Draco Meteor vs. 0 HP / 0 SpD Assault Vest Palkia: 270-320 (84.1 - 99.6%) -- guaranteed 2HKO
252 SpA Palkia Spacial Rend vs. 0 HP / 0 SpD Assault Vest Palkia: 206-246 (64.1 - 76.6%) -- guaranteed 2HKO
252+ SpA Fairy Aura Xerneas Moonblast vs. 0 HP / 0 SpD Assault Vest Palkia: 264-312 (82.2 - 97.1%) -- guaranteed 2HKO