Yes, HP Ice doesn't affect the Speed IV's, and the speed tier Cobalion hits when it runs Jolly is quite crucial as it allows it to outspeed mons like Mega Gardevoir and Garchomp.
I think he means if it is worth dropping either SpA (Jolly) or dropping some SpD (Naive)
4- SpA Cobalion Hidden Power Ice vs. 252 HP / 4 SpD Garchomp: 164-196 (39 - 46.6%) -- guaranteed 3HKO
4 SpA Cobalion Hidden Power Ice vs. 252 HP / 4 SpD Garchomp: 180-216 (42.8 - 51.4%) -- 53.9% chance to 2HKO after Stealth Rock
4- SpA Cobalion Hidden Power Ice vs. 252 HP / 0 SpD Gliscor: 180-216 (50.8 - 61%) -- 43.8% chance to 2HKO after Poison Heal
4 SpA Cobalion Hidden Power Ice vs. 252 HP / 0 SpD Gliscor: 204-240 (57.6 - 67.7%) -- guaranteed 2HKO after Poison Heal
4- SpA Cobalion Hidden Power Ice vs. 252 HP / 0 SpD Landorus-T: 176-208 (46 - 54.4%) -- 3.1% chance to 2HKO after Leftovers recovery
4- SpA Cobalion Hidden Power Ice vs. 252 HP / 0 SpD Landorus-T: 176-208 (46 - 54.4%) -- 95.3% chance to 2HKO after Stealth Rock and Leftovers recovery
4 SpA Cobalion Hidden Power Ice vs. 252 HP / 0 SpD Landorus-T: 192-228 (50.2 - 59.6%) -- 78.5% chance to 2HKO after Leftovers recovery
In my opinion Naive is better than Jolly just by looking at the calcs above.