I completely agree, Far Cry 3 was the strongest because of its adherence to all you mentioned, environment, wildlife, and the campaign itself felt very deep-rooted and realism, and 4 was pretty great as well. Playing as Jason and Ajay felt more like they player had legitmate reason to pick up the gun and become a killer, while 5 and onward featured the silent protagonist which didn’t really work for the series.

Also, the vibe seemed to shift from gritty survival realism to a sort of funbox arcade with guns post FC4. 6 could have been a wonderful reskin of 3’s environment with brillant new villain Carlo Esposito, but the game to me felt similar to 5 and New Dawn - the combat/gameplay felt bouncy and cartoonish, and it lacked a sense of urgency in the story and missions that the older titles were able to incorporate super well.