Li Shenron
Legend
I loved that old UA Battlesystem rules article, it was my favourite UA ever, and I totally want the 2017 expansion rulebook to contain a finalized mass combat system.
But we have to understand and accept that D&D is not primarily a mass combat game. It is quite the opposite i.e. a small-team mission-based game, where each character covers a different role in a way that makes each player feel important for the success of the team.
As such, a mass-combat rules system is a wonderful addition, but it's still an addition. It is supposed to be used occasionally, and as such it doesn't need to be "perfect" or especially realistic. If a campaign revolves heavily around mass combat, it is a better idea to pick a standalone well-established mass combat system of another game and play that instead, perhaps alternating between such system and D&D characters, without much regard to inconsistencies between the two, rather than trying to fit a round peg in a square hole.
That said, for me who still want to play D&D but would enjoy the occasional large-scale battle (like in LotR), the UA Battlesystem was good enough, although I'd welcome any improvement.
The key point is to accept that D&D rules serve their purpose well, and if the Battlesystem also serves its own different purpose well, then inconsistencies are of secondary importance. If we don't accept this, we risk waiting 50 years for a system that would handle both purposes perfectly, if it is even possible at all.
It might be ultimately more fulfilling to try and accept those inconsistencies, and find some narrative ways to mitigate them.
For example, while a D&D Fireball can kill every target in its AoE when playing in D&D mode, it doesn't have to work the same way when playing in mass combat mode. That's because we can think of rules as models, and models have a purpose: once you're beyond the purpose, it is the model who should be set aside to reveal what is the reality, rather than sticking mindlessly to the model and blame a reality that "doesn't match" with it.
So the D&D Fireball rules aren't the reality of the fireball. They are the model which describes what fireball does when you are in a typical D&D fight i.e. few enemies. The reality might be that once you have a lot of enemies, they provide cover to each other, and so the fireball is not anymore as effective as this model suggests, and it doesn't in fact kill everyone in its AoE.
Same thing applies to the action economy. Turns are designed assuming there isn't much stuff going on at once around the characters, so they can effectively cast a spell every 6 seconds. Mass combat mode can change that assumption, and so we don't have to stick with the "one spell per 6 seconds" principle.
