We can agree to disagree. I think we are going round in circles.
This would be fine, if you didn't immediately go back to making arguments.
I was reminded today of how protagonists and antagonists in slasher films get knocked about and yet we’re told increased hp in the game breaks horror.
This is a bit of a strawman, as it's not just a few more hp when you level. Being knocked about isn't solely a matter of hitpoints, either. We're treading into dangerous ground, here, on what hitpoints mean, and that's going to expose another avenue where a lot of popular thinking on the nature of hitpoints goes directly against horror tropes.
At the end of the day, while some horror stories feature the bookish academic struggling futilely against stronger powers, translating texts and identifying artifacts, that kind of character isn’t much fun to play. The reality is that the kind of 80% exploration pillar horror isn’t much fun for most people... in any campaign system.
In truth, horror probably goes with a 30/30/30 split rather than the 50/25/25 split of a standard campaign. That’s not a problem, 5e works fine in the circumstances. Exploration has always been more about Character choices than powers anyway.
Exploration is often undercounted in games, as most games feature a huge amount of exploration that just gets discounted as play. Exploration is every time you look in a new room. Every time you engage lore to find out new things. Every time you investigate a trap. It's a huge amount of play that usually just gets subsumed in description and narration. Playing some other games that do this differently really exposes just how much of typical D&D play is exploration pillar and also how much of this is ignored as part of narration.
As for the splits, I don't think either of those splits is particularly useful or descriptive of what normal or horror play looks like. Way too much variation. I will say that horror most likely features much less combat than normal play, because horror requires combat to be scarier and the 5e combat mechanics cut against that.
I see little gain to trying to narrow the definition of horror in order to exclude fun elements of the game. I guess people who don’t think Alien is horror will always struggle with 5e horror campaign - partly because their expectation of what is horror excludes too much. I also think more Cthulhu games resemble Alien in plot if not style than these would people care to admit.
I think Alien is absolutely horror, and a good example of it, but I disagree with your assertion that the 5e system is good for horror games. I wouldn't use 5e to replicate an Alien-style game, I'd use a different system that is designed to work the horror story beats. 5e isn't built to do horror beats, it's built to do, well, D&D, which is close to swords and sorcery and heroic fantasy and does those well. I've laid out specific points of the 5e system that cut against horror tropes and those haven't been addressed. Instead it's a rapid-fire what-about featuring things that are either strawman beating or unrelated to the 5e system, like setting mood with props or pointing out that protagonists get beat up. These don't make your point that the 5e system works well for horror.
To me, the fundamental thing that 5e doesn't do that's necessary for horror is have flexible stake setting mechanics. Combat, again, explicitly limits stakes for most actions to a very narrow set of possible outcomes which aren't conducive to horror. Removing hp doesn't speak to horror well. Outside of combat, the D&D stake setting is usually "do I do this specific thing I'm attempting" which, again, isn't very good stake setting for horror. Horror really thrives when stakes can be set that go past the immediate action or involve things that aren't currently in the framing of the scene. You go to open the door, fail, and that means that you do open the door, it's a scary hallway that looks like it's going to collapse, but also the creature comes around the corner behind you -- this pushes the action into a series of possibly snowballing hard choices for the player and better evokes the fear of the situation. These things aren't possible with 5e mechanics, as most of that would be considered part of prep or off-camera movement of the creature by the GM. This is why I said earlier that some of the strongest options in 5e to enable horror are success at cost and fail forwards, because these can be used inside the limited stake setting of 5e to generate some of the kind of snowballing that enables horror. The options for action resolution, though, are still aimed at heroic fiction in D&D and not the wider option set of some games that work well with horror.