Has D&D ever really served this purpose? Has it ever really been a tactical combat simulator?
I find in 5e a lot of the tactics and strategies come from characters' abilities and class powers. I do think you're right that monsters could use some more interesting tactics (like 4e), but I still wonder if any edition of D&D has done this well.
Only if you add the optional rules to do so.
If you just up HPs to makes both sides HP sponges who twach each other, what's the harm of introducing optional tactics to liven up the pillowfight? Or options to remove the nerf swords?
What's the harm?