This could easily turn into a big debate, and already seems to be trying to, but let's try to avoid that, eh? I'm not going to engage in a debate on this, I don't feel it's a productive use of time. But, to answer some of the questions here:
1. No, there like won't be an option to turn off border aggression, for the same reason there is not an option to turn off special forces, AI reatreats and counterattacks, the AI potentially breaking free from a planet when you cap the command station, etc. Waves and CPAs are one thing, as they are major events of a very specific sort, but these various other AI mechanics are just how the AI gets any form of self-directed mobility. If it's too hard, I suggest a lower difficulty.
2. In many ways, snake and other similar maps actually aren't any harder than the more open maps; and in some fashions they are easier than, say, Grid. But that's assuming that you play certain styles of strategy (lots of deep raiding and planet hopping, etc), which clearly isn't the case here.
3. Playing against a train master is also somewhat shooting yourself in the foot as far as border aggression, etc, goes, because the train master is slightly more defensive than average, and on average the AI is fairly defensive. If you want a really castrated opponent, play against Mad Bomber with no waves on; that guy hardly gets any reinforcements, and as noted earlier there's no recompense to the AI for the no waves modifier.
4. To the idea that you ought to be able to play a casual version of AI War at any difficulty level: that's seems kind of silly. If you're playing casually, you're meant to lose at various higher difficulty levels. As in, otherwise there wouldn't be any hardcore difficulty levels at all. Difficulty 10 is not meant to be won by any more than the top 1% of the hardcore strategy gaming population. Why? So that those folks have something to do if they come play this game, since there is no pvp play.
On the flip side, difficulty 1 is so incredibly easy it's meant to be winnable by anyone with even the slightest casual interest in the game. At diff 1 the AI hardly gets any reinforcements, almost never gets the tempo, makes loads of stupid mistakes all over the place when it does attack you... etc. If you're looking for essentially just a puzzle that you can go solve by going out into the galaxy and stomping on planet after planet without ever being attacked or there being any consequences, I suggest difficulty 4 or 5, or possibly lower depending on how easy you want it to be. I'm not being patronizing; that's part of what those difficulties are for.
5. Lastly, there has always been a time component to AI War, even aside from waves. The longer you take, the more the AI reinforces, and with border aggression that also has some consequences for you defensively after a certain point. The higher a difficulty you play on, the more you see this effect; it's almost not noticeable on difficulty 1, and on difficulty 10 you must keep moving constantly. You can play really long games if you want, at any difficulty level, but you just have to be prepared to deal with the consequences of what the AI does at any given level. At the higher levels, letting your game go extremely long is going to make the AI extremely powerful.
I hope that information is helpful. I think there are plenty of options to offer the sort of game style you're looking for, but I think you'll have to give up on the higher difficulties and the narrow maps if you're wanting a super slow, casual experience. You're specifically enabling settings that are counter to that sort of experience at the moment. Again, hope that helps.
