It is true that eliminating the more=better would solve the unbalance towards attacking even better.
I personally just don't like that concept, it would completely change the game, and it is called civ4.... I hate it when attacking is not worthy at all. It just doesn't have to be so much better then building.
First of all, just so I didn't come across as a cIV fan, this just about the only part of the game that I think got better in 4. I can't stand the bias against the military part of that game, and how it got so minimized and bland. Just so you know.
Second of all, it doesn't make attacking
entirely unworthy, it just means you need to think for a second before deciding to level another civ. Wars are (supposedly) expensive, and I don't see this modelled in civ3. Heck, with the influx of new cities, in many cases a war will actually boost one's economy. This is entirely wrong.
I have a friend on another civ site who often refers to the civ3 more-is-better problem as a "paint-spill simulator". Essentially, he points out that the main object is get big (spread the paint), and once you get big, it's really easier to get even bigger (spread the paint still more) until you rule the whole world (the map is painted in your civ color). Again, this isn't how it should be. Your proposed solution doesn't do anything about this problem, either. Because, although wars would suddenly become more difficult, it would still allow you to become bigger, and once you're bigger, it suddenly becomes easier to win yet another war, which makes you bigger and allows you to win yet another war, and so on. Giving the defense a bonus will slow you down, but it will not alter the end outcome one bit.
What i suggested, is not an idea specifically on civ and it's AI. It is a principle for strategy games in general.
By making defence stronger, you will need more attackers to conquer the same amount of land. More investment for the same reward = less efficient and a better in line with the return on making other investments.
I see. But as we're on a civ forum, we're going to apply it to civ, regardless of what other strategy games have done with it. And I still say it won't work. Primarily because of the AI. As I said, we have to apply this to civ, and not strategy games in general.
Many games have defence towers that are multiple times as cost efficient as attackers,
You mean like, radar towers?
I somewhat agree with you on the whole bonuses-helping-the-attacker argument, but really, what causes this is that while wars in history were primarily fought over terrain, in civ, the wars are fought over cities. If you want good terrain to benefit the defenders and not the attackers, you need to have the defense occupy the good terrain themselves. That can't happen in civ, though, because if they move out of the city to do so, then the attacker will simply bypass them and take the city. Not realistic, but that's how it works in civ, as you know. The only way to really solve this problem is to decentralize the city as a site of commerce and production, and that's not going to happen any time this century either.