Well that's interesting because in my current crowded game (on Deity) 3 AI's boxed me in and then were super-friendly and I got alliances with all 3 without even trying that hard. One of them was even Hungary.
Of course it's always easier for the human to play the diplo game playing as the human against ai. Though certainly not on deity. I haven't played a deity game in a while. So my comments aren't based on that. I was mainly referring to AI against AI. And as in my game below, they did wipe each other out, though mostly early on before walls went up.
But this thread did inspire me to play another Greatest Earth map with all civs like the old vanilla days. I had to get a mod to disable loyalty though. I forgot to enable a mod I think fixes the lack of civ jersey colors, I screwed up on that one. So many civs are "invisible". It can be a challenge fighting a war against invisible units, but that somewhat makes up for the lower difficulty level.
I played as the U.S., rough rider Teddy. I figure I won't conquer too much, it would make things too easy. But I did want go get all 50 states. I capped it off by using Beowulf capturing an Aztec city on the Hawai'i homeland and completing all 50 states. Sounds about historically right.

Starting this last war around year 1800 actually sparked a military emergency, and a significant regional war. I was already at war with Maori and the Aztecs to conquer Hawai'i, but then Cree and Canada joined in. Attacks from all sides. I also like this map because the AI builds a lot of Navy ships, and Navy is somewhat important on it. So I had a good naval battle in the pacific against several AI's. Only bad thing is Alaska isn't really represented on the map, except by a mountain, so my Alaska is kind of in Siberia. But I wanted a city up there in case there was oil (there was not).
I didn't include Eleanor since loyalty was turned off, and it wouldn't be fair to her, I had Cathy and Vicky instead. And I didn't include multiple leaders from the same civ, so only one Greece, India, etc. I think I ended up around 45 civs, I'm not exactly sure. I didn't keep track. Germany, Greece, and Alexander were taken out early on. Looks like Alexander had no place to settle, and settled on the Arabian peninsula. Babylon was wiped out as well. Looks like either Persians never built a city or I forgot to include them. I also didn't include Sumeria since Babylon was already in the game.
My screenshot, I almost always include a Las Vegas since that's where I'm from. New Mexico was originally an Aztec city, should have razed it, it was a crappy city. Montana was originally a Canadian city. Cahokia was a city state that unfortunately was in my way. Sounds about historically right.