TwoSix
Everyone's literal second-favorite poster
Principle wise, I think I fall into a somewhat underdiscussed middle.That's simply not the case. If there are general systems, players are perfectly capable and interested in extrapolating from them. Not knowing the precise details of any specific NPC does not preclude them from making inferences from what they do know. If nothing else, a player should be able to judge that an enemy wielding a greatsword in two hands will likely do more damage per hit than an enemy wielding a longsword and a shield.
You could go even further in the 3e days. Two-handed manufactured weaponry on an enemy that is supposed to be a skilled combatant means Power Attack, which means avoiding letting the enemy do full attacks, debuffing the enemy's accuracy, or buffing your AC are all probably more effective than usual. You can imagine a step further still, with specific DCs to make knowledge checks to determine what other abilities might modify the opponent's damage, and combat actions that aren't as miserable to use as Power Attack and Combat Expertise.
There's obviously a loss of information if you render the relationship between the enemy's fictional description and mechanical output into a black box, or a CR calculation.
For monsters like a beholder or an aboleth or a nycaloth, I really don't care how the "sausage is made", stat-wise. Those kinds of monsters are built specifically to concept, and don't really have any sort of grounding in PC-facing rules.
Humanoid NPCs, on the other hand, those which have a strong fictional resemblance to PCs, I do think should follow similar build principles to PCs, although they don't have to be slavishly followed. Any humanoid opponent that's in the higher CRs is, narratively, almost assuredly an important individual within the fiction, and should be created and treated as such.