Have to agree with pretty much everything. As a big fan of Assassins Creed myself, I enjoyed (and still enjoy replaying ever so often) the original storyline thoroughly. As well as Black Flag and the stories of Connor Kenway.
But I agree with you. The captivating story, the neverending "cat and mouse" game between the Assassins and the Templar Order portrayed in the first few games is nonexistent in the latter ones. Especially in the last three games which I decided on not playing altogether. (Origins, Odyssey, Valhalla) since I do also think they're basically Witcher 3 with Assassins Creed name stamped on top. Does not have the feeling, the vibe and the stealthy aspect of the other ones.
Unity, could be awesome. Could be much, much better. (SPOILER the sudden time jump to for example, WW2 was amazing and is definitely a missed opportunity IMO. SPOILER)
To add on top of what you said about Unity, both it and Rogue bring great new angles to the story, Rogue with all that defecting to the Templars and Unity having Arno be raised by the Templar Grand Master, but intentionally not being indoctrinated by him, and also his really one sided love for Elise.
At least Unity got some story redemption with Dead Kings, watching Arno get back his will to fight after wallowing as a vagabond after the main game was pretty poignant.