Origins seems like a significant step up from the previous AC games, it feels so different (and better) to play, it might as well be a game in another franchise. Odyssey seems to be more in line with how the Far Cry sequels have been lately, which is to say, not that different. A new story and characters isn't enough to make it seem like a reasonable leap from the last game.
If the Origins team made the game in 3 years, then it really shows how talented they are.
Far Cry 5 is a huge structural and mechanical shift from its predecessors. It abandon a range of design tropes associated with FC including towers, collectibles, skinning and crafting, and a strongly paced linear story in favor of non-linear resistance gameplay akin to HFTR's Hearts and Minds system, with narrative progression dictated by everything the player does as they roam. Ultimately AC: Origins and FC5 alike owe quite a bit to Ghost Recon: Wildlands, which in turn owes a lot to Watch_Dogs 2 which in turn is derived from Far Cry 4's anecdote machine concept.
AC: Odyssey is different to its predecessor in a number if ways. It's an actual RPG with dialogue choices that have meaningful consequences, for one. And that's kind of important. The revamped quest design encourages organic non-linear exploration. While it falls back on scoping the area with your bird when you get close, rhe player is forced to look at their map and go exploring to find many objectives.
Incidentally, AC: Syndicate in 2015 was pretty different to the games before and after it. The game was structured around gang warfare, grapple hook traversal, your train home base, and carriages, which were a rather new addition to the series. These games have always introduced new ideas. Just look at how much experimental stuff was in FC: Primal, too. No guns was just the tip of th iceberg. It's just that The Witcher 3 came out in 2015 and this led to a very conspicious pivot for the AC series where it quickly changed genres across two games.