Right, so the question is, should the AI be expected to place an exceptionally high priority on attacking the human player or on winning by whatever route it deems to be most probable?
I personally spend a lot of time trying to ensure war only ever happens on my terms. To me, one should be able to pull that off fairly reliably. I agree it can be taken too far, but I'm just trying to figure out what exactly people expect from the game and the AI logic.
If we grant that the AI should be playing to win at all costs, and it calculates that warring with you will reduce its chances, how should it proceed?
I think when it comes to games you always end up having the need to compromise with different aspects.
For example you want to make the game realistic but you also want it to be playable and more importantly "fun".
You want the game to be challenging but you also don't want it to be too frustrating.
So from one side it only makes sense that the AI doesn't start a war on someone who isn't an easy mark, but if no one ever DoW on the player the game becomes boring.
Just like you I tend to build my army to deter attacks from the AI, so I do expect the AI to not attack me carelessly. But if I plan my defenses, build an army and prepare for an attack the whole game and that attack never comes, isn't that underwhelming and disappointing?
I don't think the AI should target the human player specifically but if it never was at war for a long time it should consider the option to find an enemy and attack it, only extremely peaceful civs should never go at war no matter when.
Choosing weakly civs make sense from one side but from the other side you are just leaving alone the most dangerous civs, so in the end they will win while you did nothing to stop them.
In my opinion the AI should act like this:
Ancient era: focus on expansion and development
classical era: attack bordering civs if existing. Prioritize the best territory for land and resources. In this era civs shouldn't be too smart and they shouldn't shy from war even against strong enemies.
medieval era: attack religious competitors if religious or like above if not. Again religious fervor should work against better judgement.
Renaissance era: Stronger focus on exploration. Settle on land rather than conquer, if land available. Prioritize weaker civs for conquest. Religion should still play an important role but a bit less than before.
Industrial era: Religion doesn't matter anymore. Avoid war with strong enemies, prioritize weak enemies and expansion on unsettled lands.
From this point onward AI should act depending on Ideology
Freedom: Focus on peaceful victories but when someone starts a war they should build armies and attack them as their top priority. They should liberate cities rather than annexing whenever possible.
Order: Focus on production and development, they should have a medium tendency to start wars against civs with other ideologies but never among themselves.
Autocracy: Focus on amassing huge armies, attack without fail the enemy that they hate the most or the weakest one. They should attack even when their chances of victory aren't high.
I think this would ensure a more varied gameplay and a better chance of getting into wars followed by phases of relative calm if you built your civ strong enough, then going on a world war scenario once you get into the late game.
And all this while still retaining a fairly high chance to create strong and durable alliances (In G&K and Vanilla you simply couldn't trust anyone and that was also wrong.)