Ummmmm...in what context would theological combat make sense for anything but religion? Also this exact mechanic pretty well exemplifies how Christianity spread through Rome.
I thought my post was quite clear in distinguishing between the
theme and the
mechanic. A video game (and elements within the game) is the marriage of both. Great games are made when the mechanism fit the theme perfectly making for a fun (the job of the mechanism) and engaging (the job of the theme) experience.
Here, Theological Combat is the theme applied to this mechanic of resolving conflict between units to affect cities nearby. Unfortunately, like some marriages, this is not a good match and it raises some issues:
1. Real life missionaries/apostles focus on the citizens not other apostles, in majority of the time. Some debates have occurred but not at the scale implied in the game. Heck most debates occur within religion groups that cause separation rather than between different religions.
2. "Health" of an apostle makes no sense. Do apostles get weaker to debate after they engage in one? Do they get intellectually tired? What does their healing mean when they skip a turn? But the mechanism of fighting requires some skill and some health bar so we got to have that.
3. Yes, the lightning bolts. Since the mechanic requires some fight animation, all the theme can offer is this or old people yelling at each other. Silly, but I admit it's down at the bottom of my worry list. But as we can see from this thread and others like it, it's raising concerns with people when other elements of this video game haven't. Because almost all other elements in the game have married both the theme and the mechanism a lot better.
4. My biggest concern: Lack of unit upgrades. The theme cannot offer enough ideas to keep the mechanic fresh over the age of the game. So now we are stuck with a mechanic that will be repetitive throughout the game.
I understand all the good reasons why the mechanism of Theological combat was added. It definitely will give us plenty to do in peaceful times. But it is doing so in a silly way when it did not need to.
The devs could have kept religion the way it is in civ5 with the other improvements to the beliefs system. And introduced the mechanism of non-military units having conflicts with each other to give us something to do in peace, but dressed it up as something else. I suggested merchants doing bidding wars, the OP suggested spies in secret missions. There are plenty of themes that you could have applied to this and kept the game fun and engaging at all fronts.