consider taking Keep on the Borderlands and literally just playing the combats in some sequence. There's no gameplay at all of any kind between the combat sequences. The GM literally concludes a combat, and immediately shifts to the next site of combat and says, "Roll initiative," and instructs the players that all expended resources are immediately available again.
Very much like just playing 5 or 6 Heroclix combats in rapid succession, with no intervening roleplaying, exploration, etc.
If you played Keep on the Borderlands in this fashion, have the rules of D&D provided anything that any other set of wargame mechanics could not? Could you not swap out the D&D combat rules for the Heroclix combat rules, or the Gloomhaven combat rules, or the Journeys in Middle-Earth combat rules, or the Mythras combat rules, or the GURPS combat rules, and achieve largely the same experience?
Sure, some of the underpinnings and choice / resolution factors change, but at the end, either you've conquered all of the combats as a team, or you have not.