In my current game India steamrolled his entire continent. I think we need to be careful about short sample size.
At release I have to say I never experienced AIs even taking each other's cities - it was a very long time before I saw one being wiped out, and that was because the defeated AI had launched all its units at me and so had nothing to defend itself with.
In general the AI remains rather poor at taking out entire civs in my experience, and I think in only one game I've ever played have as many as two civs died to other AIs - but that was one of the last games I played pre-GS.
In GS itself I've seen AIs take one another's border cities with some regularity, and when they fail to it's more an issue of simply not attacking a vulnerable city than a case of not having enough units or not attacking in force when they od choose to attack. In the late game in my last game the Khmer were able to defeat a somewhat half-hearted French attack on New York, but then I wasn't able to take the city either.
I can't conclude anything about the AI's ability to take out civs in GS from their failure to do so in one game (or three, as mentioned above), as it was a very rare occurrence previously. It was also rare - although not to the same extent as in Civ VI - in Civ V.
Also, I’m thinking of changing the values in the diplomacy actions XML so it’s waay tougher for the AI not to hate you, I love the idea of a relentless military AI
I think the new friendly AIs are a consequence of the grievance system. In normal play a nonaggressive human player won't do anything to upset AIs so they'll mostly be friendly - if you want to upset them just do things that you'd expect to annoy them, like seizing city states, breaking promises etc. (though I repeatedly broke promises not to spy on my allies and they always agreed to a new alliance).
My sense is that the grievance system is too forgiving - not enough things cause grievances (for instance settling nearby or rejecting a trade deal could cause a minor grievance), and grievances decay too quickly and/or are set at too low values (especially with cassus belli, which pretty much remove grievances altogether for declaring war). For once this is not an AI issue - as far as I can tell the AI responds appropriately based on what the grievance level is telling it to do.
This of course is a common issue with GS, and Civ VI in general: every new mechanic is set to be too forgiving for the player. Climate change has minor impacts, disasters are more often a positive thanks to added fertility than a negative. I really think Firaxis' in-house pool of playtesters is too limited.
That the designers play on low difficulties is one thing - knowing how to design the game and how to play it most efficiently are different skill sets, and their job necessarily means they need to play at a level where they will succeed most of the time in order to fully test new mechanics at all game stages. But the streams indicate that they have one or two primary 'drivers', and they play at difficulties no higher than Emperor.
They really need both better and weaker players testing the game at all difficulties, because the poor difficulty scaling is the core problem rather than the fact that the default difficulty is fairly low. Comments from the devs on the stream imply to me that they genuinely don't appreciate that Immortal and Deity aren't much more difficult than King or Emperor.