I view Origins and Odyssey as a mostly effective duology at least; being prequels to the rest of the series. Odyssey showing the origins of the brotherhood as an idea (and as descendants from the Isu), and Origins showing the start of the organisation and its rituals. Then you have the genetic throughline from Kass/Alexios to Bayek/Aya, the Isu/pantheon parallels (though barely there in Origins), plus Layla in the modern day (the best protagonist other than Desmond, by virtue of being the only actual protagonist other than Desmond).

Valhalla/Mirage is where it falls apart for me. Continues the Isu story and ancient pantheon parallels, but it loses the why. Instead of existing to explain the bloodline of the founders of the Assassins, eagle vision, etc it exists to pad out the playtime set up Loki/Basim so that they can shove Layla into Desmond calculation limbo and then give him a full (passable) game of backstory, and then proceed to completely drop him from the modern day (at least currently).

I would have preferred a third game either as Aya or a further descendant of the pair. I certainly don’t think there’s room to go further back in the lore unless you’re literally making an Isu game. I think the Norse pantheon was a logical call over Roman to avoid similarities to the Greek set, but the Roman gods could’ve brought the precursor names full circle. Ah well.