You're right in that Hyper Offense teams don't care whether they're at 100% hp or 4% hp, but here's the thing. Banded GW users like Lando-T and Mence have priority that can take almost any mon found on hyper offense straight from 100% hp to 0% hp before they can do anything about it. Suddenly you care, because a majority of your team is invalidated if that Lando/Mence gets in and anything that does survive a hit will not appreciate taking another. If you want to get your Lando check in, you basically have to sac a Pokemon or carry a dedicated counter to it like Unaware Rhyperior. That's a team slot you are dedicating to beating something so overcentralizing and strong that it 6-0's your team and demands a counter, and you're forced to give up running another offensive threat in that slot.
Pinsir and Altaria do similar things, but only if they're given the chance to set up a Swords Dance. They don't have as much immediate power and you can pressure them to where they don't get a chance to set up. There are mons on Hyper Offense teams that can still check these threats by taking an unboosted E-speed and then KO'ing.
252 Atk Aerilate Mega Pinsir Extreme Speed vs. 0 HP / 0 Def Terrakion: 211-250 (65.3 - 77.3%) -- guaranteed 2HKO
252 Atk Choice Band Landorus-T Brave Bird vs. 0 HP / 0 Def Terrakion: 348-411 (107.7 - 127.2%) -- guaranteed OHKO
Gale Wings gives you far less options to offensively check the users of it because the priority is so much stronger.
Pinsir and Altaria do similar things, but only if they're given the chance to set up a Swords Dance. They don't have as much immediate power and you can pressure them to where they don't get a chance to set up. There are mons on Hyper Offense teams that can still check these threats by taking an unboosted E-speed and then KO'ing.
252 Atk Aerilate Mega Pinsir Extreme Speed vs. 0 HP / 0 Def Terrakion: 211-250 (65.3 - 77.3%) -- guaranteed 2HKO
252 Atk Choice Band Landorus-T Brave Bird vs. 0 HP / 0 Def Terrakion: 348-411 (107.7 - 127.2%) -- guaranteed OHKO
Gale Wings gives you far less options to offensively check the users of it because the priority is so much stronger.