I don't think the AI should be prevented from abusing conscripting city populations. It's a logic thing to do, and I've done it myself a couple of times ("fight to the last man!!"), and it would significantly weaken it vs humans.
As for transport ships... yeah the AI simply doesn't know how to handle amphib ops, imho. In every mod I've seen (even the original game) at most it just picks one transport, loads it up and charges with just that; other transports may come latter on, but only singly. I think it's just that he A
I part is not
I enough to realise what amphib assaults are and that they require massive brute force; so, at most we get these "commando raids", or nothing at all. It requires inteligence to know how to use these units. A similar problem exists with submarines: stupid AI sub runs into one of our ships, it attacks and declares war, instead of simply going around...
"Siege units", you mean artillery? I build lots, as in
dozens. Then I used them to punch up defenders down to 1hp before attacking, or to soften up those giant army stacks the AI sometimes makes. But I do get the problem of defender vs attacker; untill tanks appared, defense vs attack was actually quite balanced. Perhaps one way is to create strong (but slow) AT units, with little offensive power but strong defense and a defensive fire value. So, for example, assume a tech called "
Early tanks" is now available, 2 new units would pop up (these values are made up):
Tank 12/5/2
AT 2((5))/10/1
For earlier units, try to balance the defense/ofense values:
Pikeman 1/6/1
Hussar 7/2/2
This might increase the use of artillery to soften up the enemy before an attack.
Since we are discussing unit costs and their use, I have another: nuclear weapons. In pretty much every mod I've played, they are
easy to get, far too easy. And the AI sees no problem in using them as just another weapon. I think the cost of both this tech, and the weapons involved (specially missiles) should be vastly increased, as in 500% or more, to reflect their importance and maybe curtail there use.