To be fair, dice give inconsistent results too.
They give random results. Consistently so over enough rolls. Well, if they're fair dice.
Ok, but what about the case where there is no mechanical benefit to a monster? What if I give an Ogre an Int of 14. Is that worth a CR increase?
I suspect the solid mechanical benefit could be a guideline. A +2 to checks is nothing to sneeze at, a +2 to hit or save DCs is a big deal. It's a judgement call, but that's something to base the judgement on.
Like so many things, it's likely to be situational. Put the unusually-bright Ogre in a situation where what you judge to be 'good tactics' can give it a meaningful advantage, it'd make an encounter tougher - it might be tougher in the same sense that being outnumbered is tougher - the encounter is harder, but the CR and exp values of the participants are unchanged. In that case, the question would be moot.
How should I quantify the differences in how the Ogre performs in an encounter? And why are we limiting this to a discussion of Int?
I brought up WIS & CHA, as well.

But the mental stats are potentially troubling as we make decisions for our PCs & monsters that'd be influenced by those stat were we blessed (or cursed) with the real IQ/perception/personality corresponding to those numeric abstractions.
If I increased a Lich's strength to 18, it's unlikely that I would increase it's CR, as that has no mechanical effect on its combat ability.
I'm not sure why a lich would have an 18 STR, but, the lich has a nasty attack just for touching you, one that grappled you would likely be that much nastier. Just a random thought.
Likewise, what if you increased an Ogre's Wisdom?
More likely to spot you if you try to sneak past is.
What if you increased an Ogre's Charisma? I can think of all sorts of things that might play out slightly differently based on different stat abilities, but there is no way to measure the impact on combat ability, and therefore it really doesn't seem like it should have any bearing on Challenge Rating.
It's not like CR is that hard a number, but, yeah, it'd bear on the difficulty of the encounter more on the CR.
Some DMs are simply tactical illiterates.
Actually all DMs are tactical geniuses outside of tactics implicit in the game mechanics (like focus fire - well, until they overrule said mechanics), because they judge what tactics work and how well. If the DM rules that wearing pink tu-tu's and quoting Emerson is tactical genius, then when his high-INT Ogres do it, they get advantage on all their attacks.
I think the only approach that really makes any sense is to have CR guidelines that are based on mechanical effects, because those are the effects that can be measured and compared unequivocally
Sure. Of course, being a tactical genius, or more generally being smart, could be given mechanical effect, in the monster's stat block.
FREX:
Masticator is smarter than his brother Crunch, and uses surprisingly good tactics in battle, whenever he moves into melee with an enemy that was not adjacent to him at the start of his turn, he gains Advantage on his first attack.