And this is the sort of prescribing narrative I don't care for. The ogre is an ogre that has an objective existence.
Seriously, it's imaginary. It has no objective existence, or even subjective existence. What it is, what it can do, how tough it is, whether it exists - all entirely arbitrary.
Maybe the PCs fight it, maybe they befriend it. Maybe they win, maybe the ogre wins. Maybe they leave it alone, but re-encounter it several levels later.
I mean, if they befriend it, and make a real difference to it, some of it's stats might change, like it's alignment. If they win, obiviously, it's stats change, as it's dead. If the ogre wins, maybe it takes an NPC Warrior level or some equivalent. If it's several levels latter, the PCs stats have certainly changed and the ogres might have.
And when the demigod and the blacksmith decide to face the ogre together? What then?
For playability, I'd stat the blacksmith more like a minion, but that's a variant I've toyed with, not part of the system.

Practically, you'd use the minion stats, the blacksmith would loose initiative badly to the demigod, who would one-shot the ogre.
Most reasonably, you wouldn't run a game for a 4th level and 16th level PC.
For completeness: that an Ogre has 1 hp or 100 hp or whatever is obviously not a setting fact (unless your setting is some fourth-wall breaking comedy thing). It's a mechanical state of affairs that is only relevant to game play.
True, hp are an extreme abstraction that delivers a decent compromise between playability and genre emulation (and gives simulation a miss, tbh). As unsatisfying as they often are as simulation, narrative device, or balanceable game element, they are one of the better ways of handling PC durability that I've seen, and certainly simpler than those I might judge superior. For handling monsters/NPCs/objects they have some issues. But for PCs, arguably a good mechanic.
I'm not sure a minion mechanic would help the issue we're seeing here with 5e. 5e has fighters scale primarily in terms of damage and primarily by getting extra attack. That makes them very good at single-target DPR because of the AC, hp, and damage bonuses have always worked in D&D makes multiple attacks against a single target, frankly, a bit broken.
Thus, if you tune a high level fighter to keep pace when grinding down a single high-hp target (the most potent use of multi-attack, the class's most potent feature), the class will fall behind when trying to mow through many targets (and indeed, everywhere else but single-target DPR). It's like requiring the wizard to divide up his meteor swarm damage among the enemies who fail their saves, instead of doing the full damage to all of them...
.