>>16512392252+ SpA Rotom-W Hydro Pump vs. 252 HP / 0+ SpD Assault Vest Escavalier: 100-118 (29 - 34.3%) -- 3.7% chance to 3HKO
252+ SpA Rotom-W Hydro Pump vs. 0 HP / 252+ SpD Assault Vest Escavalier: 79-94 (28.1 - 33.4%) -- 0.1% chance to 3HKO
It's a 1% difference and HP gives you physical protection as well, and using an adamant nature makes the gap even smaller.
I'd love to explain why having HP and defensive stats that are closer together is better, but someone named derp lol who uses txt spk would probably not understand parabolas.
Although for anyone else who cares, even Doublade, with a massive defense of 150 and an Eviolite, benefits *entirely more* from HP than defense, rather than *slightly less about 40% of the time, and more otherwise* like Escavalier does.