Same here Jox, i couldn't help but to notice similarities between the two, but personally, i really like both films, each for different reasons. I always found it funny to see comments on reviews of Men Of War from others who feel the same way. And let's just say, there were more than few people who liked Men Of War more than Avatar

However, i don't think i would say how Sayles beat Cameron when it comes to writing similar story. Reason for that is, and i could be wrong here so feel free to correct me, but SAFE PLACE was written around '83 or something, right?
Well, around 1981, either before or around the time he first started developing the story and screenplay for Terminator, Cameron also came up with something similar to Avatar. Although, from what i heard thanks to someone who talked with Randall Frakes himself, it wasn't fully developed until 1991, when Cameron was still busy working on Terminator 2, which is when he and Frakes wrote the story treatment and titled it SCREAMING STEEL. It was a futuristic action thriller taking place in ruins of what's left of L.A., and it was about teenage streets gangs on what i can best describe as "flying motorbikes", similar to Air Bikes from Judge Dredd (1995), fighting evil and corrupt police and army run by "rich elites" from the city.
The main hero was basically someone who just like Nick from Men Of War, and Jake from Avatar, finds himself in situation where he at first is not sure about working/living with "other side", but more times he spends with them and learning their ways, and even falls in love with female member of the gang, he realizes he was on the wrong side before and he joins the teenage gang and eventually leads them to battle the actual bad guys of the story, which he was a part of before.
Frakes wrote the first draft of the script, and then Cameron hired at least few more writers to write other versions based on their story and Frakes's script, but the film was never made. However, i have to say, just based on 1991 draft by J.F. Lawton i have, Cameron definitely took a lot from it for Avatar.
Just some fun unproduced movie history trivia for you Jox. Hope you're doing alright, and wish you lot of luck and joy in 2023!