The main things I
don't like about regicide, is that you never get anything from the razed towns, and all the Wonders tend to get burned down as well (though if you're trying to prevent an AI-controlled clan from winning the War Council vote, that's not necessarily a bad thing!).
If I had programmed Civ3, then rather than wiping any remaining towns off the map, the regicide option would sell off all their Cultural improvements (with the gold going to the victor), reset their Cultural value to zero, and then flip them to a neighbour, according to the existing probabilities (i.e. based on the relative distances to the Palaces, and/or Culture strengths).
Or
at least treat the towns as if they'd been razed, so the victor would get some Workers(Foreign) out of it.
Otherwise if you kill the "king" of a clan their cities immediately disappear from the map (which is lame

).
In the early game, before the runaway-AI has emerged (the Takeda, in most of my games so far), it's usually still possible (and preferable) to wait to kill the Daimyo until
after you've captured the rest of his clan's towns (often only 4-6 per clan), so that only the enemy capital gets burned down.
In the late game though, it's frequently preferable to just go straight after the Daimyo. Not just because the relatively high unit D-values likely mean that you'll need the vast majority of your forces just to crack the capital (unless you have Ninja, but even then you still need a stack tall enough to take out all the Sam Archers first); but also because the Civ3 AI's Settlement-suckiness puts it at even more of a disadvantage on that map than on, say, a Large 4byo Pangaea.
The large swathes of low-food Hills and no-food Mountains make the remaining irrigable flatland even more precious -- but the AI nonetheless continues to prioritise access to resources over every other consideration: freshwater, coastline, etc. I frequently find towns built on Cows/Wheat, or on Plains/Grassland surrounded by Hills -- so I find it can be quite ...
satisfying ... to watch all those growth-stunted cities evaporate.
And by that point I usually already have (or can cash-rush) a bunch of Settlers(Foreign), out of the towns I captured earlier in the game, which makes it very easy to resettle the freed area quickly -- while also putting my new towns in better positions than the AI did.
f the Sengoku mod has 3-unit armies, it is broken already. Afaik the AI never bothers to load a second unit into an army.
It probably will also load a defensive unit and have a useless one-unit defensive army parading around.
Agree with you on this though. AFA
IK, the AI never uses its MGLs to make Armies at all.
So if one was going to mod the .biq (and I have), the battle-created unit should probably be a 1-unit capacity Army with a substantial HP-bonus (+8 HP = 2 vet units, seems reasonable). The AI would almost certainly still load theirs ineptly, but at least the human-controlled Armies wouldn't be
quite so OP...