One of the odd things about D&D is how the various skills systems its had have sat alongside combat, rather than be a part of it. That d20 might be a core mechanic, but it gets used differently in the pillars of exploration, combat and interaction.
So for War Stories, I considered breaking that cycle and pulling combat into the skills system. But then I didn’t, and that’s because a game about soldiers makes the notion of a discreet combat system fit perfectly. The government makes sure soldiers know how to fight, all the same way. So does my combat system, kinda, and I use a parallel system when out of the firefight.