First, I don't think HP are purely a gamist and narrative construct.
GNS is BS, anyway.
hp are very abstract covers it.
They represent a huge bundle of factors like luck & skill, divine grace, size and toughness, plot armor, etc, etc... by the same token, hits that do damage needn't so much as touch the target, and one attack/round can represent many individual blows.
Whilst abstract, they represent something diegetic.
I mean, diegetic in it's native jargon means a sound in a film that the characters portrayed by the actors are meant to hear as part of the story - even if it's added in post, and the actors never hear it. TBF, it's also a narrative thing.
hp can - and do rather well, actually - represent the 'plot armor' that heroes have in genre. I mean, it explains the weird tendency to fall from great heights without injury. They're a lot poorer at modeling actual physical injury.
Some things being harder to kill is a thing that actually exists in the game world, or at least that's how I'd run it.
There's no need to run it that way (or not to), of course, because hp are so very abstract.
If you do want to have a thing that exists in the game world explain why minions are defeated with a single blow, you could go with morale. They're facing greatly superior foes, one smack and they give up.
Nor is that the only way you could rationalize it, if you felt the need to rationalize powerful heroes scything through lesser foes quickly.
(I mean, 'fast combat?')
Second, I'm not really a fan of such predestined purpose. That seems railroady to me. Ogre is an ogre, and what their purpose is, if any, will emerge in play. Their stats are assigned to represent who they are, not to fulfil some predestined narrative role.
I mean, it's arguably railroading a monster, which, like the DM controls them, so they are on whatever rails he lays down for them, prettymuch by definition.
"Railroady" is used as a bad thing in reference to DMs erroding player agency, taking choices away from them or making those choices moot.
And third, as a player, does it feel to you that you defeated a powerful monster if you kill a one HP monster? Because it doesn't to me.
It's clearly not meant to. Not a monster that's powerful, relative to your PC, anyway