My post here is a complete tangent.
You ever have a moment when someone says something, and a rather different point falls into place in your mind. That just happened.
No, it doesn't mean you have to play less than intelligently. Another alternative is to play your spellcasters intelligently, but understanding that they have never heard of hit points and armor classes, and cannot do average-damage-per-round calculations to figure out optimal choices. They have qualitative knowledge of what happens, but not all the quantitative information the player has.
Way back when, playing 1e, we had a couple of folks in the party who could cast Fireball. 33,000 cubic feet of flaming death, that would shape itself to the space, if it couldn't just be a sphere. We, the players, having been told we were in a space with 10' ceilings, could count map squares and know how far back down a corridor a fireball backblast would come, and thereby whether party members down that corridor might take damage.
But, would the characters know? They didn't have tape measures, or even so detailed a map as we players did. We instituted a coupe of rules - no counting the squares individually, and no announcing exactly how many hit points you had left unless the GM asked you.
Suddenly, what counted as "intelligent" spellcasting became much different - less about outright calculation, and a whole lot more about quick risk assessment.